747 classics, flap 10, 100,000 lbs error equates to 15 knots. I have taken the time to memorize a few numbers, because we use this new fangled computer program to figure out all our speeds, and like any computer; $hit in,$hit out! I don't want what happened to them to happen to me. The old charts worked for many years, and they will continue to be my backup.
I was an engineer for many years, and the 100,000 lb mistake is a common and classic mistake. I encourage pilots to memorize a few max weight numbers, and ask yourself; does this look reasonable?