Or a Standing Order or Direct Debit book.
I used to work in a bakery in the days before tills told you what change to give, this was only in the early 1990s, not the 1870s I hasten to add, so I had to be good at mental arithmetic as we had to add up manually and calculate change, the till didn't do it for us.
So it's drilled into me and I still find myself doing things that completely blow the minds of younger people in shops and bars. For example I once toddled up to the bar, quite pissed and asked for 2 pints, which I knew would cost £6.50. I had about 4 quid change in my purse and a £20 note and I didn't want more change so I gave the (probably teenage) barman £21.50.
He looked at the money, looked at me, looked at the money, looked at me, repeat a few times more and eventually typed £21.50 into his till, when of course, it told him that I needed exactly £15 change.
He would have looked less shocked, surprised and impressed if I had walked away with the two pints balanced on my head. 