I came across this challenge while editing a video of mine, and found it to be quite a challenge. I used to calculate it via the VCR method (see below, from Ebonite), but with the lack of an analogue video tape at home things have become complicated.

What I did to get closer to the truth: making a hi res camera shot from behind, close-up on the hand and on the lane so that the arrows are clearly to be seen, the front 15'. Added tape to the ball from fingers to PAP.

Then, after making some releases and watching them on the PC in slo mo, I counted the ball's rotations "U" from the release of the thumb up to passing the 4th arrow. I also got my strike ball speed "S" through the speed measurement of the lane, and with some math I came up with a simple formula for RPM calculation:

RPM = U * S * 5,9844

- "U" is the revolutions and fractions from ahnd to 4th arrow, or an average of multiple shots
- "S" is strike ball speed in mph (measured with stop watch or from the lane mechanics)
- 5,9844 is a constant factor to convert speed and time to RPM, based on the front 15' of the lane.

From my video I got a ball speed of S=23.21 km/h=14.36 mph, which is about 0.7 sec for the front 15' of the lane, and 3.25-3.5 revolutions of the ball. Putting my data into the formula I came up with about 300RPM for me - which sounds plausible to me since former "classic" VCR measures 1 year ago came up with 250 PRM, and I definitively have developed some revs in the meantime.

Maybe this is a little help to you out there, since VCRs are becoming a rare tool these days

Are there any other halfways reliable methods out there? I got the feeling that there is a very broad and probably subjective range in RPM determination, ranging from CATS measures to the naked eye?

Any comments, opinions, experience?


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CALCULATION OF REV RATE (from BR.com's FAQ section/Brian Pursel: Product Manager, Ebonite)

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.
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DizzyFugu - Reporting from Germany
Confused by bowling? Check out BR.com's vault of wisdom: the unofficial FAQ section

Thanks, Bob. My problem is that I do not have any camera equipment on my own - I "share" the input of a bowling fellow with a high res digicam and only receive the uncut mpgs therefater. So, left to my own devices, I tried to make up a robust method.

Nevertheless, the numbers I got from the video and my calculations sound realistic when I look at your sample numbers, so there seems to be hope that I might be correct.

Even though I still have doubts about the formula, since it would mean that a higher speed would increase the rev rate? That does not sound too good, maybe back to the drawing board...
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DizzyFugu - Reporting from Germany
Confused by bowling? Check out BR.com's vault of wisdom: the unofficial FAQ section

The only problem with the "VCR" method is that different balls will give you different rev rate calculations.  Low R.G./High diff balls will give you one reading since the ball is going to rev alot more off of your hand, and a plastic ball will give you another reading(which is more true) since there is no weightblock to get the ball into a quicker motion.

Since you are in Germany, I'm not sure what kind of camps/clinics are availible to you, but I would suggest that everyone who wants to take their game to the next level to attend at least two sessions on Ebonite's BowlersMAP software, SportsMOtion program, or some type of Kegel/C.A.T.S. clinic.  There is so much information you can find out about your physical game.
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-DJ Marshall
...The Twelve In a Row Pro Shop