I started school in 1968 and thus learned elements of pre-decimalisation and post decimalisation: money, weights and measures. I keep things in my mind for comparison such as 2.54 cms to an inch, 39 inches to a metre, 1,609 metres in a mile, 1.76 pints in a litre and 2.2 pounds in a kilogram. A little bit of mental maths usually brings me to a close approximation of reality should it ever be required.
I was never any good at remembering the old notes and coins though save for thruppenny bits.