Decimal converters and calculators

A selection of decimal converters
A selection of decimal converters. Top to bottom and left to right: Shoppers' guide, a decimal pen, Decimal Adder, Decimal Currency Calculator, Parker Decimal T-Ball, Decimeter

Britain switched from pounds, shillings and pence (sterling) to decimal currency in 1971. People wanted to make sure that they were not diddled. Young people found the change to decimal currency easy. Older people still thought in old money.

The most confusing part of the process was the changeover period. Some shops marked up prices in sterling and others in decimal. You could pay in either and got either decimal or £sd coins in change.

Ahead of Decimalisation, the Decimal Currency Board produced a booklet called 'Your guide to decimal money'. It had a forward by the Chairman, Lord Fiske. He explained that getting used to decimal currency would be easy. The guide was sent to every household in the country. It contained some useful tables to make conversion easy and information about issues such as change, cheques, shopping, telephone kiosks and banking.

If you wanted something more convenient than a table in a book, there were a number of devices on the market that might have helped.

1971 was the decimal year, but it was just before the digital age. Although the first pocket calculators went on sale 1971, they were too late to help with decimalisation. Instead there were a variety of mechancial devices to help with the changeover. A couple of months after D-Day, most went in a drawer and were forgotten about. This a a selection:

Parker Decimal T-Ball

Parker Decimal T-Ball, close up
Parker Decimal T-Ball showing the conversion table.

The Parker Decimal T-Ball was a Parker Jotter with a window and a special refill. The refill had convertion tables printed on it. You could see the table through the window. There were four tables which could convert 1 to 12 old pence to new pence or 1 to 20 shillings to new pence.

If you used the pen carefully you could convert any amount up to £1 in old money to new pence. But it did not work the other way around.

The pen came in a choice of six colours. They cost 18 shillings and 6 pence or 92½p as Parker conveniently pointed out in their 1969 and 1970 adverts.

Parker marketed them as a business gift. You could order fifty or more and get a quantity discount. Parker could also put a message on the barrel so clients knew who the pen was from.

They were also an ideal Christmas present for children at Christmas 1970. After 1971 you could at least still use the pen. I wonder how long they kept making the special refills for them though?

Decimal converter pen

If you could not afford the Parker, or your bank manager did not give you one, there was always this striking yellow and black biro made in Italy. It converted amounts in shillings and pence to amounts in decimal. It did 0 to 10 shillings plus any amount in pence. There was also a column for 19 shillings and an amount in pence.

Decimal currency calculator

Decimal Currency Calculator
Decimal currency calculator

This was a more sophisticated device. It was a circular device with a table. It allowed you to look up amounts in new pence and convert them to pounds, shillings and pence. It could also work the other way.

There was a hole in the top of the device suggesting you could wear it around your neck. It may have been intended for use in shops and businesses. The clerk could give the customer an accurate conversion.

Shoppers' guide

This was an aide memoire style shopping list. It had a list of common shopping items, such as bacon, bread, meat and tea. There was an 'old pence' to 'new pence' conversion table on one side and an imperial to metric conversion table on the other side.


Decimeter 1968-1971

The Decimeter was the best of the small mechanical devices. It was invented by David Silvester Evans. It received UK patent GB 1232861 on 19 May 1971.

The Decimeter used two wheels to let you convert between decimal and £sd and vice versa. It could handle amounts up to 20 shillings or 100p It was available in several colours.

From March 1969 people were warned through the small ads of the Daily Mirror and Daily Express that 'money will soon be a problem without the Decimeter'. It was slim enough to fit into a pocket or a purse.

It went on sale in February 1969, two years before D-Day with a patent pending. The Decimeter cost 7/6 initially, but the price dropped to 5/6 (or 27½ new pence) by 1971.

Decimal Adder

The Decimal Adder allowed you to add amounts in decimal currency. It did not do any conversion between decimal and pounds, shillings and pence.


Olivetti Prima Summa 20 adding machine
The Olivetti Prima Summa 20 adding machine could handle both sterling and decimal

If you needed to do some serious adding up in decimal, Olivetti offered five different adding machines in 1970 that could handle £sd and decimal. This Prima Summa 20 from 1960 was modified in the second half of the 1960s to cope with both decimal and sterling. It was designed for small business or home use. You could get one with Green Shield Stamps.

A switch at the bottom changed from £sd to decimal. Presumably you switched it over in 1971 and never switched it back.

It could add or subtract and could do multiplication with some skill on the part of the operator.

This one is quite happy to do pounds, shillings and pence is still going strong today. We used to use it to add up our bills.

I love the mauve colour scheme, this was unique to the dual currency models. Olivetti was known for making their calculators attractive. The design was by Marcello Nizzoli.

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Retrowow - vintage, retro and social history
Retrowow - vintage, retro and social history