How Allies used serial numbers in Nazi tanks to figure out the German tank production per month

In WWII Allied forces admitted that Nazi tanks were superior to their own tanks. The key question was: how many tanks Nazi Germany was able to produce per month. The Allies tried intelligence gathering: POWs, spying, etc. Via this method, they estimated that from June 1940 to September 1942, the Third Reich manufactured 1,400 tanks each month. Ridiculous number, because the Axis powers had only 1,200 tanks during the Battle of Stalingrad. Then Allied intelligence noticed each German tank contained a unique serial number. Using this, the Allies created a mathematical model, which suggested the Germans produced 255 tanks per month. (jalopnik.com)

How Allied Forces Used Tank Serial Numbers To Defeat The Germans