How do you know how many deer you've killed?
How do you know how many sits and hours you've been in a tree?
Deer? It's not that hard, I have every set of antlers and can remember every shot, it means that much to me, and does... it's that many if not a couple more. Math isn't that hard.
And hours, again, I know how many days I've hunted, I've only missed 1 day and Sundays and it's from after work til dark plus Saturdays and vacation. Again, the math isn't that hard.