while exemplary embodiments are described herein in sufficient detail to enable those skilled in the art to practice the invention , it should be understood that other embodiments may be realized and that logical material , electrical , and mechanical changes may be made without departing from the spirit and scope of the invention . thus , the following detailed description is presented for purposes of illustration only . in one embodiment , a putting methodology , system and device is disclosed which may utilize a golf club , such as a putter , comprising an integrated specialized viewing area that may magnify the cup and superimpose or otherwise project an image in the viewing area that can be used as a point of reference to more accurately and consistently read the pace and line of the putt . in one embodiment a putter comprising at least one integral lens is provided . this lens may be used for magnifying a view image . a user may use personal experience coupled with the advantages and improvements of the device to hone their putting skill . moreover , the device may be customizable to individually suit the desires of the user . with reference to fig1 , an exemplary optical putter calibration tool is provided . in one embodiment , optical putter calibration tool 100 comprises an eye lens 10 , a beam splitter 20 , an objective lens 30 , a target lens 40 , and a target reticle 50 . in some embodiments , optical putter calibration tool 100 further comprises an illumination window 60 and / or an optical path 45 . window 60 may comprise a transparent surface allowing light outside of shaft 70 to provide light to target reticle 50 . in various embodiments , eye lens 10 may be a negative ( e . g ., concave lens ). eye lens 10 may be an optical device with substantially perfect or approximate axial symmetry which transmits and refracts light , converging or diverging beam of light . though eye lens 10 is described as consisting of a single optical element , it may be an element of an optical system , such as a galilean telescope . eye lens 10 is generally the lens most near the eye when a user is looking through optical putter calibration tool 100 . as seen in fig1 , eye lens 10 is oriented substantially parallel to the axis of shaft 70 . in one embodiment , the diameter of eye lens 10 is a function of the diameter of shaft 70 . in this manner , the width of eye lens 10 , which is generally positioned near , or in line with , the exterior surface of shaft 70 , may be no wider than the curved exterior surface of shaft 70 . with continued reference to fig1 , objective lens 30 may be configured to collect light and brings the light to focus creating an image . in various embodiments , objective lens 30 may be a positive ( e . g ., convex lens ). objective lens 30 may be oriented substantially parallel to the axis of shaft 70 . in one embodiment , the diameter of objective lens 30 is a function of the diameter of the shaft . in this manner , similar to eye lens 10 described above , the width of objective lens 30 , which is positioned near , or in line with , the exterior surface of shaft 70 , may be no wider than the curved exterior surface of shaft 70 . in some embodiments , the lenses of optical putter calibration tool 100 are permanently mounted in the optical putter calibration tool 100 , causing the lenses to have a fixed pre - determined magnification and field of view . eye lens 10 and objective lens 30 may be situated such that the focal point of the eye lens 10 is the same as the focal point for objective lens 30 . objective lens 30 may be configured to work in concert with eye lens 10 to provide a pre - selected image magnification . the pre - selected image magnification may be any suitable magnification , such as a magnification between about 1 . 5 times to about 2 times , though other magnification powers are also suitable and contemplated . for instance , the pre - selected image magnification may be about 1 . 7 times magnification . the magnification may be configured to be a function of the distance between objective lens 30 and eye lens 10 . for instance , the focal length of eye lens 10 , combined with the focal length of objective lens 30 , to which eye lens 10 is optically coupled , may determine the magnification . in some embodiments , the separation and / or diameter of one or more lens is a function of the diameter of the club shaft 70 at the mounting location . the magnification provided by the optical putter calibration tool 100 may help overcome the issue of discerning subtle pitches . also , the magnification may aid those with deteriorated or non - ideal eyesight to , for instance , discern the slope of the playing surface and / or see the cup . in various embodiments , optical putter calibration tool 100 comprises specialized channels 45 , 46 to direct light from object lens 30 through beam splitter 20 to eye lens 10 and / or from target reticle 50 through target lens 40 to beam splitter 20 . with the exception of optical enhancers , such as a lens and / or beam splitter , these channels may be free of structural interference and / or comprise properties for assisting in transmitting beams of light . with renewed reference to fig1 , eye lens 10 may be optically coupled to objective lens 30 through beam splitter 20 ( along channel 46 ). beam splitter 20 may be an optical device that splits a beam of light in two . in this manner , beam splitter 20 may be an optical element that allows part of an electromagnetic wave to pass through while reflecting the other part . with continued reference to fig1 , beam splitter 20 may be configured and / or oriented such that a first portion of a beam of light passes from objective lens 30 through beam splitter 20 through eye lens 10 to the eye and a second portion of a beam of light is “ split ” and is directed from target reticle 50 through target lens 40 through beam splitter 20 through eye lens 10 to the eye . in this embodiment , beam splitter 20 may be positioned approximately midway between eye lens 10 and objective lens 30 . the beam of light passing from objective lens 30 through beam splitter 20 to eye lens 10 may be substantially normal to the axis of shaft 70 and the beam of light passing from the target reticle 50 through target lens 40 to beam splitter 20 may be directed substantially parallel to the axis of shaft 70 ( while traveling in optical path 45 ). the focal length of target lens 40 and the scale of a target reticle 50 ( described further below ) are selected to produce a reference target of a pre - selected size . for instance pre - selected such that when viewed by the eye the target reference may exactly match the size and shape of the magnified cup . in one embodiment , the illumination of target reticle 50 is provided via a window 60 on shaft 70 of the club . fig1 depicts target reticle 50 being used in reflection with top illumination . in another embodiment , transmissive targets may be used by placing the window below target reticle 50 . in another embodiment , optical putter calibration tool 100 may comprise a battery operated light source for illuminating target reticle 50 , such as via a led 51 . in some embodiments , target reticle 50 may be coated with luminescent materials and / or self - illuminating ( depicted as light rays 52 ), such as by using a radioactive element ( i . e ., tritium ). in one embodiment , target reticle 50 may be customizable from a variety of reference targets and or selectable from a variety of reference targets . in one embodiment , this reference target may be scalable to accommodate a preferred use by the user , such as the size of the reference target may be scaled based on the preferred distance of use from the cup ( x ) or height above the ground ( y ). in an embodiment , a first target reticle 50 may be exchanged with a second target reticle 50 with different properties . these properties may include color of elements , size of elements , contrast of elements , gradient indicators , placement of elements and / or the like . for instance , to accommodate a color bind user , varied levels of light , and / or a shorter user . second target reticle 50 may be integral to optical putter calibration tool 100 such as by inverting target reticle 50 from a first side to a second side . in an embodiment , target reticle 50 may be provided by a battery powered digital display with customizable properties . for instance , battery powered digital display target reticle 50 may display a first image of a first size and first color and display a second image of a second size and second color and / or combinations thereof . in an embodiment , target reticle 50 using a battery powered digital display may display a first image of an ovoid designed to approximate the shape and scale of the direct view of the cup . this target reticle 50 may display a different second image such as , a second image of an axis with lines emanating in 45 degree increments with radiating gradient hash mark indicators . in one embodiment , first target reticle 50 may be removed and / or replaced by a non - integral second target reticle 50 , such as by replacing a card or disc . in one embodiment , the light source illuminating target reticle 50 may be removed , or turned off by removing the target reticle image 80 displayed to the user leaving the magnified direct view of cup ( or viewed image ) remaining . this may aid the user in viewing the magnified view of the cup . this removal may be by any suitable method such as covering window 60 with a covering and / or removing power to an electronic light source . in some embodiments , the relative brightness of target reticle image 80 and direct cup image 90 may be adjusted by altering the reflectivity of beam splitter 20 . in one embodiment , beam splitter 20 is a 50 / 50 beam splitter where about half of the light is transmitted through beam splitter 20 and about half of the light is reflected . this ratio may be adjusted by changing the reflectance of beam splitter 20 , such as during fabrication , for example , to a ratio of 70 / 30 , or other ratio depending on a particular application . target reticle 50 is depicted as being located below beam splitter 20 towards the face of the club on shaft 70 ; however target reticle 50 may be positioned above ( an inverted ) beam splitter 20 towards the grip of the club . in this manner , a second system with the same or different optical properties could be implemented in the same club and shaft either below or above first optical putter calibration tool 100 . alternatively , a second system with the same orientation as shown in fig1 may be located above or below first optical putter calibration tool 100 in shaft 70 . with reference to fig2 a - 2e , in an exemplary embodiment , target reticle 50 comprises an ellipsoid or oval shaped target . this target , along with the other components of the optical putter calibration tool 100 , is configured to present a superimposed enlarged target reticle image 80 over the enlarged direct image 90 ( e . g . the cup ). by comparing direct view image 90 of the cup to the location of and properties of target reticle image 80 the surface features of the playing surface can be surmised . for instance , a user may stand a specified distance away from the cup ( x ) with optical putter calibration tool 100 held at a specified height ( y ) above the ground in a line with the users ball &# 39 ; s path to the cup , where the user and the ball are on the same side of the cup ( as shown in fig3 a - 3b ). due to the golf cup being a finite diameter ( standard of 4 . 25 inches ) direct view 90 of the cup from a specific distance ( x ) and specific height ( y ) is the same if the putt and / or playing surface is flat . with this in mind , target reticle image 80 can be calibrated to be that exact shape and size as direct view 90 cup image from a pre - selected specific distance ( x ) and height ( y ). in one embodiment , the pre - selected distance optical putter calibration tool 100 is positioned away from the cup a particular distance ( element x as depicted in fig3 a - 3c ), such as between about 4 - 22 feet from the cup . for instance , the pre - selected distance ( x ) may be about 14 or about 16 feet from the cup . this distance ( x ) may be scalable and / or customizable to the user . in this manner , target reticle 50 may be shaped larger or smaller to accommodate the distance away from the cup the user desires to hold optical putter calibration tool 100 . similarly , the distance optical putter calibration tool 100 is positioned above the ground is a pre - selected particular distance ( element y as depicted in fig3 a - 3c ), such as between about 3 - 6 feet . for instance , the pre - selected distance ( y ) may be about 4 . 5 or about 5 feet above the ground . this distance may be measured at the level of eye lens 10 in shaft 70 of the club rather than the base and / or club head of the putter . this distance ( y ) may be scalable and / or customizable to the user . in this manner , target reticle 50 may be shaped larger or smaller to accommodate the height ( y ) the user desires to hold optical putter calibration tool 100 above the ground , such as to accommodate users of differing heights . in one embodiment , target reticle image 80 is substantially the same size and substantially the same shape as direct view image 90 of the cup when the cup is viewed from the pre - selected distance ( x ) and height ( y ). if direct view image 90 of the cup and target reticle image 80 substantially overlap as perceived by the user , the user can infer that the playing surface is substantially flat . however , if ( as depicted in fig2 a ) target reticle image 80 is to the right of direct view image 90 of the cup , the user can infer that the golf ball &# 39 ; s tendency is to break to the right from its current direct path lie and that the playing surface slopes to the right . an example of what direction is meant by “ breaking to the right ” is depicted in fig2 a . conversely , if ( as depicted in fig2 b ) target reticle image 80 is to the left of direct view image 90 of the cup , the user can infer that golf ball is likely to break to the left and that the playing surface slopes to the left . an example of what direction is meant by “ breaking to the left ” is depicted in fig2 b . if ( as depicted in fig2 c ) target reticle image 80 is above direct view image 90 of the cup the user can infer that the playing surface slopes uphill . if ( as depicted in fig2 d ) the target reticle image 80 is below the direct view image 90 of the cup , the user can infer the playing surface slopes downhill . after the user has calibrated the speed and line the user can step down to the low side of the cup holding the optical putter calibration tool 100 a prescribed distance ( x ) and prescribed height ( y ) and use the viewing area to confirm what is known in the trade as the “ fall line .” by moving along the low side of the cup until image 90 of the cup is level with projected target reticle image 80 a users &# 39 ; read of the playing surface can be verified ( as depicted in fig2 e , and 3 c ). for instance , along this path , the direct view image 90 of the cup and target reticle image 80 should substantially overlap completely . additionally , in some embodiments , the target reticle 50 and target reticle image 80 may comprise gradient indicators ( see fig4 a - 4b ) such as markings , dashed lines , dots , crosshairs , posts , circles , ovoid shapes , scales , chevrons , hashes , grid markings , and / or targets . in one embodiment , these gradients indicators comprise dashed ovoid shaped rings proportional to direct view image 90 of the cup . gradients indicators may be below , to the left and / or to the right of a solid or dashed ovoid shape and when compared with direct view 90 of the cup may provide a means of calibrating the amount of break in the playing surface . for instance , direct view 90 of the cup as viewed from a pre - selected distance ( x ) from the cup and a pre - selected height ( y ) above the ground in line with the path of the ball to the cup may provide a means of calibrating the amount of break in surface features the lie of the path of the ball to the cup . for instance , if direct view 90 of the cup overlaps 2 gradient lines a user can surmise that the slope of the playing surface is more severe than if direct view 90 of the cup overlaps a single gradient line . a user may calibrate the ball speed needed to overcome this slope of the playing surface based on personal experience . in some embodiments , a calibration booklet 91 may be provided to allow the user to document the amount of force or pace needed per gradient marking in their putting practice , such as prior to the round . this calibration booklet 91 , may comprise paper and pen , and / or may comprise an electronic computer application , such as an application operated by a processor on a mobile device or hand held computing unit . this calibration booklet 91 may be an application saved to a non - transitory computer readable medium . the calibration booklet 91 may be used to record how much force per gradient line of break is needed to correct for various playing surface variations . in some embodiments , the gradient indicators in various locations comprise different colors or line thickness to represent and assist in delineating relative position . additionally , the gradient indicators may comprise stadia marks . these stadia marks , also called stadia lines or stadia hairs , may be crosshairs on target reticle 50 and target reticle image 80 that allow stadiametric range finding . also , the target reticle 50 may be subdivided into sections . for instance , ( as shown in fig4 b ) target reticle 50 comprising a target image segmented into quadrants by segmenting lines or segmenting colors . in one embodiment , target reticle 50 may comprise engraved lines , embedded fibers and / or an image directly on eye lens 10 such as a laser image ( thus eliminating beam splitter 20 , target lens 40 and a down - shaft target reticle 50 ). in various embodiments , the target reticle 50 may be replaced by a computer - generated image superimposed and / or holographic image on a screen or eye lens 10 ( similarly eliminating beam splitter 20 , target lens 40 and a down - shaft target reticle 50 ). a user may calibrate the ball speed needed based on personal experience with stadia mark readings . in an exemplary embodiment , direct view image 90 ( such as the cup ) can be focused by moving eye lens 10 nearer and further from objective lens 30 . this movement of eye lens 10 may be performed by actuating a focusing mechanism allowing movement of the channel in which eye lens 10 is mounted , without needing to manipulate eye lens 10 directly . in some embodiments , and with reference to fig5 a - 5b , optical putter calibration tool 100 comprises visual indicator 425 to aid the user in determining the make - up of the playing surface . for instance , optical putter calibration tool 100 may comprise a level indicator such as a spirit level or bubble level . in another embodiment , the indicator may be a floating body , such as a floating plane or other shape . the visual indicator 425 may be oriented in any plane . for instance , the orientation may be horizontal ( level ) or vertical ( plumb ) or a combination thereof , such as with a floating t or cross shape . in this manner , a user could use the level indicator rather than the balance of the club , or straight edge of shaft 70 to determine if the club is being held in the proper orientation . the user may compare the top surface of the cup and / or playing surface surrounding the cup to the results of visual indicator 425 directly . a user may compare the known level straight edge or marking on the club shaft 70 to the surface level of the cup to infer the surface features of the playing surface . in one embodiment , rings 435 ( or notches ) may designate proper orientation of the bubble or floating plane if the surface was level . also , a user may use the visual indicator 425 to properly hold and orient the club while applying the optical putting system . in some embodiments , the spirit level may comprise a bulls &# 39 ; eye level . the spirit level may be used in place of or in addition to the optical elements such as the galilean telescope and collimated reticle features of optical putter calibration tool 100 . in one embodiment , optical putter calibration tool 100 may comprise a level indicator such as a laser indicator . this laser indicator may be horizontal ( level ) and / or vertical ( plumb ). this laser indicator may be presented simultaneously with a direct view of the cup ( or with a magnified direct view 90 of the cup ). in another embodiment , the laser indicator may be displayed in a separate window . though the components and features of optical putter calibration tool 100 may extend beyond the diameter of the standard putter shaft , in various embodiments , optical putter calibration tool 100 components are designed to be contained within the dimensions of the standard putter shaft 70 . in this manner , a user holding shaft 70 might not notice shaft 70 comprised optical putter calibration tool 100 until further visual inspection of shaft 70 . in various embodiments , optical putter calibration tool may be integral to the putter , such as with a partial shaft , a half shaft , or full shaft top and / or bottom extension . in various embodiments , optical putter calibration tool may be designed as an insert into a golf shaft , such as an aftermarket reconfiguration of an existing putter . in various embodiments , optical putter calibration tool may comprise coupling members 415 to be press fit and / or fastened via glue , or epoxy into a shaft and / or partial shaft of a club . coupling members 415 may be on the top and / or bottom of optical putter calibration tool to couple with a partial shaft with grip , a partial shaft with club head and / or a partial shaft portion . for instance , coupling members 415 may be round segments shaped to mirror the inside dimensions of a club shaft . in this manner , optical putter calibration tool may be inserted into an existing club by removing an equivalent portion of the existing club shaft and inserting optical putter calibration tool in the equivalent portion of the existing club shaft &# 39 ; s place . in one embodiment , this does not alter the physical length or diameter of the existing shaft . in various embodiments , a ranging device may be built into optical putter calibration tool 100 . for instance , the ranging device may be configured to determine the actual or approximate distance optical putter calibration tool 100 is from the cup and / or the distance optical putter calibration tool 100 is above the ground . thus , optical putter calibration tool 100 and / or imbedded rangefinder may utilize lasers , stadia marks , displays , memory , power sources , and / or the turning of a calibrated wheel . for instance , in one embodiment , optical putter calibration tool 100 may direct a beam of infrared light such as a laser at a target . when the pulses are directed at a target and then reflected they are captured by receiving optics . by measuring the time from transmission to reception the rangefinder may calculate the distance to the target . the aforementioned lenses may be made of any suitable material . for instance , any of the lenses described above may be made from a molded plastic , glass , polycarbonate , trivex , and / or aspheric material . any of the aforementioned lenses may be treated with anti - reflective coatings , scratch - resistant coatings , ultraviolet treatments , polarization and / or photochromatic treatment . any of the aforementioned lenses may be high index glass or plastic lenses . any of the aforementioned lenses may be customized to accommodate the eyesight of the user such as by replicating a prescription . in some embodiments , images as seen through the optical putter calibration tool 100 , such as the image provide to the viewer through eye lens 10 , can be recorded as a picture and / or video onto a storage device , such as an internal or removable memory via an internal image capture mechanism . in one embodiment , this image may be compared to a verification reading taken on the fall line , such as on a display integral to the club . there are a number of considerations involved in optimizing the design of the optical system . important variables include the separation of the lenses , such as the distance between eye lens 10 and objective lens 30 , the desired magnification of optical putter calibration tool 100 , the distance optical putter calibration tool 100 is placed in front of the golfer &# 39 ; s eye when in use , the lens diameters , the field of view of the optical system , and the minimum distance of optical putter calibration tool 100 to the cup . the field of view is a measure of how much of the green surrounding the cup is seen when looking through the system . given these considerations , one skilled in the art of optical design would be able to analyze these tradeoffs to optimize the system for the intended purpose and within the overall system constraints . with reference to fig6 and 7 , exemplary optical putter calibration tools , comprising a viewing area that may be clear or transparent and reference target image , are provided . the reference target image may be in the shape of an ellipse . according to various embodiments , the reference target image may be within the viewing area as in reference target image 240 or be removably affixed to the exterior of the viewing area as in reference target image 340 . for instance , reference target image 240 may be physically embedded and / or etched within the transparent shaft . reference target image 240 may be any material between a front surface of the transparent shaft and the rear surface of the transparent shaft . reference target image 240 may be physically embedded and / or etched within the transparent shaft . for instance , reference target image 340 may be physically etched in to a surface , such as a front or rear surface , of the shaft . the viewing area is integral to the shaft of the golf club . the viewing area section of the club may be inserted into shaft 70 as in optical putter calibration tool 200 ( fig6 ), for example using coupling members 415 . the viewing area may also be integrated into shaft 70 as in optical putter calibration tool 300 ( fig7 ). according to various embodiments , adding the viewing area to shaft 70 does not change the overall dimensions of the golf club . according to various embodiments viewing area 240 , 340 does not involve adding external attachments . all parts of the club are fixed , and the club including the viewing area is one unit . therefore , a golf club comprising optical putter calibration tool 200 and / or optical calibration tool 300 may comply with the rules of the united states golf association and the rules of the r & amp ; a ( golfs governing body ). as disclosed herein , the reference target image 240 , 340 may be calibrated to mirror and / or overlap without extending beyond the perimeter of the shape and size as the size and shape of direct view 90 cup image from a pre - selected specific distance ( x ) and height ( y ) on a flat playing surface . according to various embodiments , optical putter calibration tool 200 or optical putter calibration tool 300 may be positioned away from the cup a particular distance ( element x as depicted in fig3 a - 3c ), such as between about 10 - 50 feet from the cup . this distance may be any desired distance . for instance , the distance may be a distance where plumb bobbing is suitable or desired . for instance , the pre - selected distance ( x ) may be about 15 feet from the cup . similarly , optical putter calibration tool 200 or optical putter calibration tool 300 may be positioned above the cup at a particular distance ( element y as depicted in fig3 a - 3c ), such as between about 4 - 7 feet . this height may be any desired height . for instance , the distance may be an eye level of the user . alternatively , it may be at a height the user prefers to plumb bob . for instance , the pre - selected distance ( y ) may be about 5 . 5 feet above the cup and / or the ground . the distance ( x ) and height ( y ) may be scalable and / or customizable to the user . in this manner , reference target image 240 , 340 may be shaped larger or smaller to accommodate the distance away from the cup the user desires to hold optical putter calibration tool 200 or optical putter calibration tool 200 , respectively . in one embodiment , the reference target image may be replaced by a second reference target image that better corresponds to the view of the cup from the desired distance and height for surmising the prescribed path of the ball . with renewed reference to fig2 a - 2e , by comparing the view of the cup , the direct image view 90 , through the viewing area of optical putter calibration tool 200 and optical putter calibration tool 300 with reference target image 240 and reference target image 340 , respectively , the user can surmise the surface features of the playing surface . with reference to fig8 a - 8e , the user can identify by the direction of the break of the putt by orienting the reference target image in direct alignment with the view of the cup through adjusting the bottom of the club to the left or right and forwards or backwards . if the reference target image is in direct alignment with the cup while the shaft is plumb to the green , then the cup is level and there is no break of the putt ( fig8 a ). if , while holding the proximate end of the club ( grip end ) in a fixed position , and pivoting the position of the bottom of the club ( face end ) to the right results in directly align the reference target image 240 , 340 to the view of the cup , then the putt likely breaks to the left ( fig8 b ). the pivot point is in line with in a plane of the ball , such as an extension of the ball location in the x axis . accordingly , while holding the proximate end of the club ( grip end ) in a fixed position , and pivoting the bottom of the club to the left results in aligning the reference target image 240 , 340 to the view of cup , the putt likely breaks to the right ( fig8 c ). if pivoting the bottom of the club forward ( away from the player &# 39 ; s body ) along this pivot point results in reference target image 240 , 340 to directly align with the view of cup , then the playing surface is likely sloping upward / uphill ( fig8 e ). if pivoting the bottom of the club backwards ( towards the players body ) along this pivot point results in reference target image 240 , 340 aligning with the view of the cup , then the playing surface is likely sloping downward / downhill ( fig8 d ). according to various embodiments , the reading of the playing surface characteristics may be verified by comparing the view of the cup with the reference target image 240 , 340 along the fall line of the ball . verification of the reading of the playing surface characteristics from the fall line assumes that the playing surface characteristics of the green along the fall line is a continuation of the playing surface characteristics of the green along the proscribed path of the ball . benefits , other advantages , and solutions to problems have been described above with regard to specific embodiments . however , the benefits , advantages , solutions to problems , and any element ( s ) that may cause any benefit , advantage , or solution to occur or become more pronounced are not to be construed as critical , required , or essential features or elements of any or all the claims . as used herein , the terms “ includes ,” “ including ,” “ comprises ,” “ comprising ,” or any other variation thereof , are intended to cover a non - exclusive inclusion , such that a process , method , article , or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process , method , article , or apparatus . further , no element described herein is required for the practice of the invention unless expressly described as “ essential ” or “ critical .”
a system and method for calibration of golf shots is provided . specifically , a tool for providing a reference target superimposed over an image of the cup for calibration purposes is provided . an optical putter calibration tool may include a viewing area and a reference target image . the reference target image may be manufactured within the viewing area or removably affixed to the exterior of the viewing area . the viewing area may be integrated in a shaft of a golf club , such as a putter , for providing a simultaneous view of the cup and the reference target image . comparison of the reference target image and the view of the cup may provide a determination of a playing surface characteristic .