How does a chronograph work?

[Elkhunter]

Didn't quite know where to put this one so here it is. I am serious and do not know. How does a cronograph work? Just curious is all.

 

[Idaho Ron]

The way I understand it the chronograph takes in light from the "eyes" on the top. When the bullet passes over the first eye the chronograph starts timing. When the bullet passes over the second eye it stops timing. Then the chronograph makes the calculations. Mine will tell the high, low, the average, and many more things I haven't bothered with. After I test a load I add it to a data base I have for rifles and shotguns for loads, patterns, and speed. Ron