I used to work in an off-licence (a liquor store, in the US) and on Sundays it would be very quiet. I invented a method to rate the busy-ness of the day: the Bohemian Rhapsody Index (BRI). Essentially, this was the number of times I could sing the Bohemian Rhapsody in full before the next customer came in. An average Sunday would round out at around two or three on the index. I think one day had a rating of seven, which needless to say was pretty high even for that shop.
I would like to say that such things are useful for keeping you sane when working by yourself in a really boring job, but I suspect that even taking the idea seriously indicates a slight slippage in the levels of sanity.