Decimal Point of No Return

Before every phone had a calculator and every till did the sums for you, changing money systems was a properly hands-on business. Decimal Day arrived on Monday 15 February 1971, when the United Kingdom and Ireland moved from pounds, shillings and pence to the decimal system. In theory, it was tidier. In practice, it left a lot of people peering at price charts, checking conversion tables and doing the sort of mental arithmetic that could make a small purchase feel like a maths exam.

This Kingston Four-Rule Pocket Calculator is a lovely relic from that moment of everyday confusion. Proudly marked “Empire Made, Redg. in G. Britain” and “Made in Hong Kong”, it is a non-battery calculator that looks both ingenious and baffling to modern eyes. One side handles addition and subtraction in £.s.d, while the reverse has slide-rule scales for multiplication and division.

Its purpose was simple enough: help people work out old money against new. Each new penny was worth 2.4 old pence, which meant some conversions landed awkwardly. An old price of £7 10s 6d became £7.52½p, hardly the sort of thing most people could do quickly at the counter.

At a time when electronic pocket calculators could cost hundreds of pounds, this modest little machine offered a cheaper answer. Today, it is wonderfully outdated – and all the more charming for it.