I wish I could claim the credit. Sadly I can't remember who I borrowed this idea from, but I have to say it's made the whole process a lot quicker and simpler.
I stole my use of it from Finaryn when he mentioned it was his method over on the OD&D Discussion forum. I don't know if it was his own creation or, like so much else in the hobby, it came from somewhere else and just spread.