He claims he dose it by "cauculating" on his own instead of pure memory but yeah i am sceptical too.
Well i either do "calculation" on myself in my mind which takes me quite some time or i just simply trust traders so i always take an account with myself just in case. Most often i make cauculation and prepare my money before i go to seller. Talking about that i always make sure every single cent i have is wisely spent. So if product is 6,47 € i will give precisely that amount of money.
Altho i often use automatic seller. Those new machines where you do everything yourself when buying. They are birlliant. Anyway multiplications like 10×10 are no problem. I got screwed up when i need to "cauculate" fast those variants like 6 x 8, etc.
LOL yeah in school i did that all the time.
Sometimes it takes me extra awful alot of sec's.