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Measurement of the diameter and the roundness of golfballs using the GBMD (Golf Ball Measurement Device)



1 Stainless Steel Frame
2 Adjust Screw
3 Adjust Nut
4 Calibration Device
5 Measurement Surface for Golf Ball
6 Measurement Surface for Ideal Golf Ball
7 Alignment Window for Marker line
8 Index 1/4 Turn Adjust Screw


The GBMD can be used for different measurements. Check the minimum diameter of a golf ball of 42.67 mm (1,680 inches) as specified in regulations prior to use of the ball and avoid a possible disqualification. Determine the diameter of any golf ball up to an accuracy of about 3/100 mm, which is 1,188/1000 of an inch (1/4 turn of adjust screw = 1 shift) and test the roundness of golf balls. Easily compare diameter and roundness of several golf balls and set up marker lines in the middle of the ball.  

Ensuring the minimum diameter

  1. open the housing in an upright position
  2. remove the GBMD and the calibration out of the aluminum housing
  3. remove the calibration device 4 und and store it into the rubber tray of the lower housing portion
  4. turn the adjusting nut 3 counterclockwise until end position
  5. place the golf ball from the top into the housing onto the spherical measurement surface 6
  6. press lightly on top of the golf ball. Can it be rotated easily by hand the diameter of the golf ball obviously is less than 42.67 mm and non-compliant


Measurement of the actual diameter

  1. Make sure that the adjusting nut 3 is still in full counterclockwise position
  2. put the calibration device 4 from the top into the housing 1 of the GBMD
  3. hold the GBMD between thumb and middle finger firmly and fix it the Calibration object 4 by pressing the index finger on top of the calibration device
  4. turn the adjust nut 3 clockwise into the housing until the adjust screw 2 touches the underside of the calibration device
  5. remove the calibration device out of the GMBD and put it back into the rubber tray of the lower aluminum housing without changing the position of the adjusting nut. The GBMD now is calibrated completely on the smallest possible diameter of 42.67 mm
  6. put the golf ball into the housing of the GBMD and again slightly press your finger on top of the ball. It can be just pressed slightly onto the surface 5 of even harder until it touches the surface 6 of the housing
  7. turn the adjusting nut 3 clockwise by a quarter turn steps (shifts) in into the housing until the adjusting screw touches the bottom of the ball and then keep turning as long as required until the golf ball can be turned by hand into at least one direction. Remember the amount of quarter turns.
  8. the number of quarter turns (shifts) made during this process will be used to determine the diameter deviation by looking into the deviation sheet below.The range T1 (equal to a maximum of 4/4 turns) describes a deviation of the Diameter of max. 5/100. Thus you would have an acceptable golf ball. Total Diameter: 42.67 mm + 0.05 mm = 42.72 mm (allowable minimum diameter + measured deviation = absolute diameter) You can personally define your own acceptable tolerance in diameter. The better your handicap, the closer you should define your tolerance to section T1 shown in the sheet.

      * value of the amount of shifts:

  1. 0-4 quarter tunrs: excellent ball (pro and scratch golfer)

  2. 5-6 quarter turns: medium ball (hobby golfer)

  3. 7 and mor quarter turns: below average ball (driving range ball)

  4. *values are to be individually interpreted by each player. Even a medium quality ball might be used by hobby golfer without serious negative effect on the game, since the average devience caused by skill might be bigger than the devience cause by manufacturing toerances





Measurement of roundness

You have previously determined the diameter by turning the adjustment screw clockwise until the golf ball could be moved in the housing of the GBMD in at least one direction. The acceptable roundness now is determined by turning the adjustment screw a further quarter more clockwise and check, if the golf ball can now be rotated smoothly in all directions. In this case, the deviation in the roundness is smaller or equal to 3 /100 mm, which is a good result (see tolerance T2 in the sheet). If the ball still can't be rotated at this stage, a Pro would not like to use this ball for a tournament. For non tournament use proceed for another quarter turn. Then the ball should be movable into each direction. Larger deviations in roundness should not be accepted and might lead to significant deviation of the direction after impact or might influence the spin rate with unwanted slice or hook as a result.

Comparative measurement of the diameter and roundness

Due to the previous measurements, the diameter and roundness of the golf balls have been determined and eventually you did decide on a particular brand or price range. Nevertheless unacceptable manufacturing tolerances can occur even within one brand. These are rather irrelevant for the average amateur golfer. A scratch golfer, and in particular, any Pro but also sort out those golf balls that have unacceptable tolerances. Anyway you might want to compare the balls of your choice by first perform the measurement according to the steps above. The measured ball thus can be rotated easily in all directions. Now insert one ball after another into the GBMD and determine if each ball can be equally easily rotate also without changing the position of the adjusting nut. Is such case the diameter and roundness of each ball is at least as good as the one has been measured at first. If the ball rotates easily in only one direction, the roundness is not guaranteed. If the rotation resistance does have in a plurality of directions, either the roundness or the diameter is generally not guaranteed. Nevertheless the absolute values using the calibration object according to the procedure above can be determined at any time.

Marking of the golf ball

Most of the golfers place value on a straight line marking on the ball. This is helpful in positioning the ball on the tee. Some golfers use the marker line to align the ball into put direction on the green. The tag line should be located in the center of the ball. The design of your GBMD enables you to mark the center of the ball by first turning the adjust screw clockwise totally into the housing. In this position the upper edge of the housing indicates the middle position of the golf ball after it has been put into it. You can use any pen thickness to mark the ball. We recommend a water resistant 0.5 mm pen. The alignment window 7 facilitates the positioning of the ball by 90 degrees to a possibly existing lettering. However, it can also be used directly for drawing a small marker line if you use a pen with a thickness less than or equal to 0.5 mm..



Your GBMD and the calibration object are made of stainless steel. Please avoid damage to both the inside of the housing and the surface of the calibration device. Always place the calibration device into the rubber tray of the lower case of the aluminum housing after using it. Any damage or even minor scratches on the hemisphere of the calibration device or the mesurement surfaces 5 and 6 of the GBMD will cause the instrument to be unusable. The GBMD can be carried in your golf bag for offshore using, but should be always fixed into the aluminum housing. The aluminum cover should be opened and closed in upright position always for securely attaching the GBMD. Even if the GBMD is resistant to moisture it should be cleaned and dried after a rain use.


If used properly, we grant you warranty according to the law. Mechanical damage to the measuring surfaces of the housing or to the surface of the calibration device is not covered under warranty..