Constants

from the inside back page of my 4 figure log and trig tables, which I learnt to use before a slide rule. I have 7 figure tables to hand in case I become a millionaire by mistake.

I cherish the counter-intuitive idea that seawater is denser than Broken Welsh Coal. Younger readers might like to know that once upon a time there was a mining industry in Wales.

And there were bronze coins in England. Bela Bartok was so impressed by the magnificent size of the penny - a humble coin - that he made a rubbing of one during a visit to London, in a letter home.

It's maths nostalgia time at the moment.