Doing big data buzzwordy jazz at my job here, and I was involved in a meeting in which the analysts are trying to come up with various metrics for counting customers that doesn't involve barcoding everyone and scanning them as they come in the door.
One way to try to get a customer count is to proxy count through certain items. It was at that point that I noticed that a sale of a whole pie was being counted as 3 people.
I helpfully raised my hand and pointed out that using 3 as an estimate for pie might not be accurate enough, and that we should probably use the more precise measure of 3.14159265358979....