Originally Posted by Bestglide

In the days of Cal the numbers actually made sense. If you take the last 3 digits of the tail number and put a 0 there it was either a DC 10 ...777 or a 764
the number 1 was for the 757-200. 8 for the 757-300 7 for the 737-700 2 for the 737-800 3 for the 737-300 and so on. So there was a method behind the madness.
now I'm not so sure?