I'm neck deep in revision at the moment, having relearned things like excess notation, floating point numbers, one's complement, two's complement, and so on, I'm doing my best to commit them all to long term memory.
One of the easier problems (working out memory requirements of a two dimensional array) I decided to do without a calculator to ensure I have things under control and don't accidentally fall on the correct answer, when suddenly it struck me: I have forgotten how to do long multiplication.
I asked my wife for help, which probably tickled her self esteem as she knew more about it than I did, but she wasn't quite sure as well so it was off to find a tutorial. I can't believe, all the shit I committed to memory, things like pulling Pythagorean Theorem out my arse when we're building a shed... and I forget something that Duncan will likely be learning in a year or two.
I know exactly how this happened, it's been almost two decades of just picking up a calculator instead of worrying about how to do it by hand. It seriously makes me wonder how much Duncan's schooling will be good for me.