Interesting story on How Allied Forces Used Tank Serial Numbers To Defeat The Germans at Jalopnik.com
Allied intelligence noticed each captured German tank contained a serial number unique to the tank. With careful observation, the Allies were able to determine that the serial numbers had a pattern denoting the order of tank production.
Using this data, the Allies were able to create a mathematical model to determine the rate of German tank production, and estimated that, during the same summer 1940 to fall 1942 time period, the Germans produced 255 tanks per month — a fraction of the 1,400 estimate.
And it turns out, the serial number methodology was spot on: after the War, internal German data put der Fuhrer’s production numbers at 256 tanks per month — one more than the estimate.
The answer to the question in the post title? A division, obviously.