In cricket What technology is used to measure the speed of a the ball delivered by bowler?
What parameter used to measure this speed?
Usually a Radar Gun, similar to what they use to test the speed of cars, is aimed down the pitch and uses a radio transmitter and receiver with the Doppler effect principle.
Hawkeye also usually uses 6 cameras and each of them measure the distance the ball has gone and how long it took and then uses this in the Speed= Distance/Time equation.
Hope that helps =D