referring now to fig1 , the measuring system 100 includes a measuring instrument 10 and a processing device 20 connected / linked with the measuring instrument 10 , in accordance with a present embodiment . the measuring instrument 10 includes a base 12 , a guide column 14 , a sliding member 16 , a digital micrometer 18 and a holding member 19 . referring to fig2 , the base 12 is a rectangular flat board . the base 12 has an essentially flat upper surface 122 , so that the holding member 19 may be flatly arranged on the upper surface 122 , so as to reduce errors in measuring . the base 12 may , advantageously , be made of a metal with high density , such as stainless steel or the like , so that the weight and linear dimensions of the base 12 together are enough to keep the measuring instrument 10 balanced ( i . e ., the base 12 beneficially acts as a ballast for the measuring instrument 10 ). a fixing hole 124 is defined adjacent to an edge portion of the base 12 . the guide column 14 may , advantageously , be made of a durable , rigid material , such as stainless steel , copper alloy , or the like , so the shape of the guide column 14 may stay the same even after repeated usage . the guide column 14 has a smooth circumference surface 142 and is configured ( i . e ., structured and arranged ) for allowing the sliding member 16 to be easily moved along the guide column 14 . the guide column 14 is configured for engaging in the fixing hole 124 of the base 12 . the sliding member 16 is approximately a rectangular block , and has a guide hole 164 and a receiving hole 166 respectively defined at two ends thereof . the guide hole 164 has an approximately similar diameter to the guide column 14 , for facilitating a slide fit therebetween . a bore ( not shown ) is defined in a sidewall of the sliding member 16 and is perpendicular to an axis of the guide hole 164 . a slot / aperture 169 is defined across the sliding member 16 so as to form two portions beside the slot / aperture 169 . the slot / aperture 169 enables the guide hole 164 to communicate with the surrounding environment . the width of the slot / aperture 169 is large enough that the two portions beside the slot / aperture 169 are moveable relative to the slot / aperture 169 . the bore is divided into two parts portion by the aperture 169 . an adjusting screw 168 is rotated into the bore to fastens the two opposite side portions of the slot / aperture 169 . therefore , the diameter of the guide hole 164 can be expanded or reduced by rotating the adjusting screw 168 . the digital micrometer 18 includes a main body 182 , a sleeve 184 and a measuring shaft 185 . the sleeve 184 is received in the receiving hole 166 of the sliding member 16 and is mounted on the main body 182 ( e . g ., the sleeve 184 is soldered / welded on the main body 182 ). the measuring shaft 185 has a contacting portion 186 at one end thereof . the measuring shaft 185 passes the sleeve 184 and extends through the main body 182 , with the contacting portion 186 extending out from the sleeve 184 . a cap 183 is mounted on another end of the measuring shaft 185 for lifting the measuring shaft 185 . a dial plate 187 , a zero reset button 1822 and a power button 1824 are set on the main body 182 . the zero reset button 1822 and the power button 1824 are located under the dial plate 187 . the dial plate 187 may display a movement distance of the contacting portion 186 of the measuring shaft 185 via pressing the zero reset button 1822 . that is , the zero reset button 1822 is configured for selectably establishing a zero reference level or datum plane , to provide a basis for measurement . an output interface 188 is formed in a shell of the main body 182 . the output interface 188 is used for transmitting dimensions data to the processing device 21 . the holding member 19 has a flat bottom surface ( not labeled ), so that the holding member 19 can be flatly arranged on the base 12 . the holding member 19 is configured for fixing a workpiece 40 . a reference - standard surface ( not shown ) is formed on the holding member 19 , which is at a same horizontal level with an upper surface of a standard workpiece 40 fixed on the holding member 19 . a cover 30 is fixed on the holding member 19 across / over the workpiece 40 . the cover 30 has a top wall 32 and two sidewalls 34 vertically connecting with the two ends of the top wall 32 . the two sidewalls 34 respectively engage in two gaps 192 defined in the holding member 19 . a plurality of positioning holes 322 are defined across the top wall 32 , configured for receiving the measuring shaft 185 . the position of the positioning holes 322 is designed according to the shape of the workpiece 40 and , particularly , to one of the positioning holes 322 positioned above the reference - standard surface . the processing device 20 , which advantageously is a programmable logic controller ( plc ) or a computer , is used to process the data from the measuring instrument 10 and show / display a testing result . the processing device 20 includes , at least , a processor 21 and a display 29 . the processor 21 has an input module 22 , a storing module 24 , a processing module 26 , and a video - conversion module 28 . the input module 22 connects with the output interface 188 of the digital micrometer 18 is set to receive data ( e . g ., measured values ) from the digital micrometer 18 via an electronic connection such as a data wire or a wireless link . the storing module 24 stores reference data and testing values transmitted from the digital micrometer 18 via the input module 22 . the reference data is , for example , a series of numbers in a range ( e . g ., 0 . 1 mm ). the processing module 26 is configured for receiving the data transmitted from the input module 22 and for processing and comparing it with the reference data , so as to generate a result . the video - conversion module 28 is used to receive the signal of the test result and transform it into a video signal . the video - conversion module 28 electronically connects ( e . g ., hard - wire or wireless link ) with the display 29 , so that the result might be display via the display 29 . it is to be further understood that the processing module 26 could be linked to a printer ( not shown ), as well . either way , the display 29 and / or the printer would serve as data output modules . in use , firstly , an user inputs a reference range value of a height of a normal workpiece 40 . the reference data is stored in the storing module 24 . the workpiece 40 is fixed on the holding member 19 , with the cover 30 mounted on the holding member 19 and over / across the workpiece 40 . the holding member 19 with the workpiece 40 and the cover 30 thereon is then placed on the base 12 . the adjusting screw 168 is then rotated outwardly and the sliding member 16 moves downward . the user moves the holding member 19 so as to let the positioning hole 322 above the reference - standard surface correspond to the measuring shaft 185 . when the contacting portion 186 of the measuring shaft 185 touches the reference - standard surface via the corresponding positioning hole 322 , the sliding member 16 is tightened up by the adjusting screw 183 . the power button 1824 and the zero reset button 1822 are pressed down in order written , and the dial plate 187 shows “ 0 ”. the height of the reference - standard surface 192 is set to zero . after that , the user lift up the measuring shaft 185 via the cap 183 while move the holding member 19 at the same time . when the measuring shaft 184 corresponds to another positioning hole 322 of the cover 30 , the measuring shaft 184 is slowly released . the contacting portion 186 of the measuring shaft 185 touches the upper surface of the workpiece 40 . the dial plate 184 shows / indicates the distance between the end of the contacting portion 186 and the reference - standard surface . when the point is lower / shorter than the reference - standard surface , the number / value is positive . otherwise , when the end of the contacting portion 186 is higher / taller than the reference - standard surface , the number is negative . the signal corresponding to the number / value is transmitted to the input module 22 of the processor 21 via a data wire . the number / value is then restored in the storing module 24 . then repeat the steps above so as to test the other points of the upper surface of the workpiece 40 via the positioning holes 322 . the numbers / values relative to the positioning points are then restored in the storing module 24 . the processing module 26 processes the numbers / values relative to the testing points of the upper surface of the workpiece 40 and generate a result . if the result is in the reference range , the display 201 will show “ pass ”, indicating that the workpiece 40 is suitably dimensioned . otherwise , if the result is out of the reference range , the display 201 will show “ reject ”, which means the workpiece 40 has one or more dimensions that are not in the acceptable range . it should be understood that the cover 30 on the holding member 19 may be omitted , and the holding member 19 may be directly moved without lifting the measuring shaft 185 . it is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description , together with details of the structures and functions of the embodiments , the disclosure is illustrative only , and changes may be made in detail , especially in matters of shape , size , and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed .