Using a radar gun can be inconvenient to carry and you may not have it when you need it.
This
thread explains how to measure the break speed using sound, but it can also be inconvenient to have a notebook computer with you.
The convenient solution I found is using my pocket PC cell phone. I always have it with me.
I run
Virtins Pocket Oscilloscope to measure the time between the sound from hitting the cue ball and the sound of the cue ball hitting the rack. The software uses the built in microphone in my cell phone as the channel 1 input. It measures to the microsecond and my cell phone samples at 96 kHz.
I input the time in into an Excel
spreadsheet (also on my phone) to calculate the speed in miles per hour. The spreadsheet is setup for the four typical table sizes and assumes the distance between the base of the cue ball and the base of the head ball is 1/2 the length of the table (head string to foot string). The spreadsheet can be easily modified to support any starting position of the cue ball. I don't want to have to carry a tape measure, so I simply fix the starting position.