the present invention is directed to the use of metal markers to inspect and better locate the surface and concentricity of a golf ball using an electromagnetic energy source , such as x - rays . more particularly , the invention is directed to the x - ray inspection of golf balls incorporating markers opaque to x - ray imaging . the use of markers , and metal markers in particular , makes it easier to particularly locate the outer surface of the golf ball for comparison with inner surfaces , such as those defined by golf ball centers , cores , intermediate layers , and inner cover layers , when imaged with x - rays . metal markers are easily “ seen ” with x - ray imaging because of their lack of transmission of x - ray energy . x - rays are high - energy photons that have higher energy and a shorter wavelength ( typically about 0 . 3 nm to about 2 nm ), compared to the energy and wavelength ( about 400 nm to about 780 nm ) of visible light . anytime there is more matter between the x - ray source and the detection film , whether the matter is thicker or just has a higher density , fewer x - rays are transmitted to the detection film , which starts off whitish and darkens as various levels of x - rays strike it . for example , bones appear lighter on a typical human x - ray image because bone is denser than the rest of the body , and in dental x - rays , metal fillings appear white , because the metal is very dense . the marker ( s ) of the present invention are opaque to x - rays and , therefore , provide a very clear and defined edge and reference point from which to measure core and layer dimensions against . because the optimal x - ray intensity for clearly discerning the core and its edges is much higher than the x - ray intensity that allows clear edge definition of the cover , the metal markers allow the x - ray intensity to be optimized for detecting the edge of the golf ball core without being concerned with seeing and using the cover as a reference point . without the markers , the x - ray intensity must be set at a compromising intensity where both cover and core can be seen ( but with reduced contrast and definition ). referring to fig5 , the x - ray image of the golf ball was taken at an intensity set to detect both the cover and the core . at this intensity , the surface of the cover appears irregular and the surface of the core is out of focus . in fig6 , the x - ray intensity is set much higher , optimized for core detection . fig6 clearly shows that , at the higher x - ray intensity , the surface of the cover is undetectable without the presence of the metal marker . preferably , one or more metal marker ( s ) are used , more preferably greater than about two , and most preferably , at least about three . the metal markers can be constructed of any material opaque to x - rays , but are preferably metal or blend of metals . more preferably , the markers are aluminum , steel , copper , or titanium . if more than one markers are present , they can be of the same or differing materials or metals . in a preferred embodiment , the golf ball can be rotated and the center of the ball calculated from the curved edge measurement . then the distance from the center to the metal marker can be calculated at predetermined intervals to determine concentricity of the core . in another preferred embodiment , the ball can be simultaneously measured on multiple axes . this improves the measurement of concentricity by making it possible to detect whether the core is shifted , no matter which direction it is shifted . referring to fig1 and 2 , when a ball is rotated about an axis to measure the eccentricity of its core , what is typically done is that the distance from the surface to the core is measured repeatedly as it rotates . the difference between the maximum distance and the minimum distance is measured and indicates how far off center the core is . however , the only eccentricity that is detected is that which is perpendicular to the axis of rotation . if the core happens to be shifted along the axis of rotation no eccentricity is detected at all . if the core is shifted at some angle to the axis of rotation , the measured eccentricity is less than the true eccentricity by the sine of the angle . according to the present invention , in order to find the true eccentricity of the core , it is necessary to measure along the axis of rotation as well as perpendicular to it . referring to fig4 , the x - ray image of a golf ball shows it being rotated along its horizontal axis . in a preferred embodiment , the ball is rotated about an axis and the distance from the surface to the center of the core is measure repeatedly . the intersecting lines indicate measurements from the center of the core to the metal markers . the difference between the maximum and minimum distance measure is taken to determine how far off center the core is . the measurements are taken along the axis of rotation as well as perpendicular to the axis . thus , there are at least two measurements of eccentricity and they are preferably combined using the pythagorean theorem . the true eccentricity ( e true ) is the square root of the eccentricity along the axis of rotation ( e 1 ), squared , plus the eccentricity perpendicular to the axis ( e 2 ), squared . referring to fig6 , because of the nature of the preferred x - ray source ( transmission type ) and the lack of focusing lenses , the quality of the image and the ability to resolve fine details is dependent on the size of the spot the radiation emanates from ( the focal spot ). preferably , the x - ray source used has a small x - ray focal spot size . in general , x - ray spot size is around 0 . 035 inches by 0 . 02 inches . the resulting “ band of unsharpness ,” seen in fig6 , is about 0 . 017 inches to about 0 . 010 inches . while this unsharpness is not a problem for imaging many types of golf balls , it can be a problem for golf balls having cover layers of less than about 0 . 05 inches . in a preferred embodiment , therefore , the x - ray focal spot size in the present invention is less than about 0 . 01 inches by 0 . 01 inches . in a more preferred embodiment , the x - ray focal spot size is less than about 0 . 005 inches by 0 . 005 inches . it is envisioned that a single lens or a combination of lenses may be used to adjust the x - ray spot size to a desired area . referring to fig7 , preferably a golf ball is clamped between a rotating cup a and a flat surface b . the cup a is made of a plastic material , intended to be relatively transparent to x - rays . inside the cup a , a metal marker c is held against the golf ball by a spring . the flat surface b is also made of a plastic material with a 0 . 06 - inch covering of aluminum that serves as the metal marker c . a piece of spring steel d that contacts the ball on its equator as it rotates constitutes another metal marker . the image analysis is accomplished using an insights ® 2000 by cognex , of natick , mass . in a first method , the edge of the core and the edge of the marker are determined using the “ find edge ” tool and the distance between the core and the marker are measured at multiple locations around the ball to calculate eccentricity . in a preferred method the core of the golf ball is located with a “ find curve ” tool . each of the metal markers is located by finding their edges , the edge adjacent the ball and the opposing edge , with a “ find edge ” tool . from this step , the middle of the marker is determined by obtaining the difference between the two edges . from this determination , the center of the golf ball core to the center of each of the markers can be determined . in a most preferred method , the core of the golf ball is located with a “ find curve ” tool . the center of each of the metal markers is located using the “ find pattern ” tool . the “ find curve ” and “ find pattern ” tools gave the most accurate and repeatable measurements . the center of the core and center of the markers are determined because changes to the x - ray intensity can alter the apparent size of an object , but do not effect the actual location . as the x - ray intensity is increased , for example , the core may appear to decrease in diameter while the center remains in the same location . it is believed that this effect results from the large focal spot size of the x - ray source ( roughly 0 . 9 mm × 0 . 5 mm ), as described above in depicted in fig3 . below is a table that compares the results of x - ray and another common method of obtaining golf ball dimensions , ultrasonic measurements . the ultrasonic measurements are of a urethane outer cover and mantle layer measured at 90 ° intervals all around the ball . the eccentricity was calculated using the square root of the sum of the squares , as described above . the identical golf balls were x - ray inspected a variety of times using the method of the invention . x - ray eccentricity is expressed as a range from the highest to the lowest value obtained . the term “ about ,” as used herein in connection with one or more numbers or numerical ranges , should be understood to refer to all such numbers , including all numbers in a range . the invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed , since these embodiments are intended solely as illustrations of several aspects of the invention . any equivalent embodiments are intended to be within the scope of this invention . indeed , various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description . such modifications are also intended to fall within the scope of the appended claims .