I know that photocells are used at the line (stage and prestage) as well as the one that prevents deep staging from a low aerokit/oilpan. Also the ones that go down the track telling you your time but how do they get your speed? I've gone down the track before with a radar detector and it doesnt read anything. How does it get your speed?

 

the track does not have "radar" it averages the last 60'feet of the run same at the 1/8. Thats why your speedometer will read a little faster than the timslip. example- you run 15.0@93 youy speedometer will probabaly read 95-96. I think there are even some tracks that average the last 66'feet.

 

Right, but how does it even get to the 93 MPH or so etc? How does it measure it? I'm guessing it can make calculations between the times you go thru the photo beams.