yeah its a couple of wires conected to the front sprocket cover. i think they calculate the number of pulses per second or milisecond (or something like that) that the nut on the spocket makes when it turns. anyway ive seen that video b4 too. im not saying he does but if you put a smaller sprocket on the front or a bigger sprocket on the back it will make the speedo read faster than the bike is actually traveling. i put a 44t rear on mine b4 and got the needle burried at 220. but i was prolly really only doing 180 if even that much.