Try this, it is from Ebonite's website (and also in the inofficial FAQ section of this website). I measured my revs this way, and it works pretty well!
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Ball reaction is a combination of the bowler's style and the bowling ball's power potential. In an earlier tip, we defined the dynamic properties of the bowling balls. Many bowlers are under the assumption that the bowling ball will create hook by itself. Bowling balls are only amplifiers of the rotational forces put on the ball by the bowler. Correct mechanics are essential to create hook potential. This month I will focus on those forces.
The bowler imparts RPM's on the ball directionally (ball speed), horizontally (axis rotation), and vertically (axis tilt). All four components merge to create the rotational force of the delivery. The degree of these components, bowler to bowler, result in the difference of hook potential.
RPM's, or revolutions applied, is the speed of the revolutions. The faster the revs, the greater the turning force is at the breakpoint. To measure RPM's you will need a low flare ball (spare ball is good), a piece of tape (4 to 6 inches long), and a video camera. Place the piece of tape running from the bowler's PAP to above the fingers. Film from behind, with a close up of the hand at the release point. As the ball is being released, stop the tape. Assign the tape a position on a clock (i.e. the piece of tape points to 10:00). In slow motion, click off 10 frames and freeze. Count the amount that the tape rotates as hours, as if it was the hour hand on a clock. Multiply the amount of hours by 15. (For example, the ball started at 10:00. After 10 slow motion frames the tape ended at 5:00, passing 10:00 once). One complete rotation around (10:00 to 10:00) counts as 12 hours. 10:00 to 5:00 (the ending position) equals 5 hours. This is a total of 17 hours of rotation. Multiply the amount of hours (17) by 15. This equals 255 Rpm's. The other way to measure revolutions is called hand revs. You will also need the piece of tape and a video camera for this. Repeat the steps for measuring RPM's, however let the ball travel 15 feet down the lane. This is the distance of the fourth arrow. Note the starting position of the tape and count the amount of times the ball has rotated using fractions, not hours. Take the total amount of rotations and multiply by 4. This equals hand revs. For example, the ball started at 9:00 and ended at 3:00, passing past 9:00 three times. This would result in 3 1/2 rotations. 3 1/2 X 4 = 14 hand revs. Why do we not count the total amount of revs the ball rotates all the way down the lane until it hits the pins? Because friction will slow down the ball speed and create additional revolutions. By using the first 15 feet, we are counting the rotations in the presence of lane oil, a very low friction environment. In our Surface Friction Selection Chart, we use hand revs rather than RPM's.
The next variable discussed here will be ball speed. The faster the ball speed, the less friction impacts the ball rolling down the lane. The less friction present, the less potential for hook. Measuring ball speed is far simpler than revolutions. You need a stopwatch and good reflexes. Measure the time elapsed from point of release until the ball hits the head pin. Take 40.91 and divide it by the amount of seconds. This will give you miles per hour. On the Surface Friction Selection Chart, "faster" ball speed refers to ball speed in excess of 17.5 MPH, "medium" ball speed refers to between 14.5 MPH and 17 MPH, and "slower" ball speed refers to 14 MPH and less.
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DizzyFugu - Reporting from Germany
Wacky style video (Oct. '06)
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