I worked at a franchised US Burger King in the late '90s. The shift manager would tell us how many fully assembled copies of each popular sandwich type to keep on hand. I never saw any charts or evidence of number crunching, but the numbers did vary based on expected traffic for the day of week and time of day, and the popularity of the specific item.

The sandwich wrappers had the numbers 1 to 12 printed on them, and you were supposed to mark the pre-made sandwiches to show when to throw them away. For example, if you assembled the sandwich at 12:15, mark the 5 to show that it should be thrown away when the clock's big hand is on the 5. Literacy not really required.

I worked back before they had installed microwave ovens, so the person in charge of coordinating the production rate had to be a good judge of the sales rate, the abilities of the grill team etc. We usually tried to time things so that we had the most food ready for lunch rush, and then let it tail off so that we didn't waste a huge amount. McDonalds had all sorts of little charts that averaged sales rates per hour, item rates within that hour etc, but a good employee running the "bin" was far better than someone who just used the charts.

I was in a pretty busy McDonalds so we were usually asked to do one more of X when doing X, or two more of Y, or 5 more of Z, ... depending on the rush. That's how we ended up trashing some.

That's because, when doing a big mac for example, it's almost as easy to make one or five on a tray. So better make 5 if you're in a rush, they will likely be fulfilled.

In cool periods we would only produce on command. So no waste. Fresh burgers.

Everyone used to say that Franchise didn't care too much about these rules (where they should), and the director didn't like getting employees from Franchise McDonalds because they had to re-learn all the hygiene standards. Since that day I avoid franchise restaurants and go only to the official ones.