How did early computers deal with calculations involving pounds, shillings, and pence?

Question

In the era before UK currency was decimal, how were accounting calculations involving pounds, shillings, and pence typically handled?

Were the underlying computations typically performed in terms of decimal fractions of pounds, in binary or decimal integer multiples of pence (or farthings!), or by keeping track of pounds, shillings, and pence as binary or decimal integers?

My research so far has only found one useful reference, and IBM System 360 Cobol specification that seems to say that computations were performed in pence and then output in pounds, shillings, and pence with a special formatting "PICTURE" See pages 117-118 at

https://www.computinghistory.org.uk/downloads/10924

Answer 1

In the era before UK currency was decimal, how were accounting calculations involving pounds, shillings, and pence typically handled?

By mostly the same machinery as in other countries - only some sprockets added like this nice Brunsviga 90T shows:

(From Wikipedia, see also this answer)

It may need a close look at display and key columns as the last column goes 1 to 11, while the third from the right only features the number 1 on all keys.

British Pre-Decimal currency was, like all Carolingian currency, structured as LSD or 1 Librae (hence the £) to be split into 20 Solidi (s) each dividable into 12 Denari (d) or in English names 1 Pound equals 20 Shillings equals 240 Pence.

This is why the display, as well, is structured as 3-3-2-1:

• 3 digits for Thousands of Pounds,
• 3 digits for Pounds,
• 2 digits for Shillings (00..19), and
• 1 'digit' for Pence (0..11)

Such variant machinery was as well created with early data processing like IBM's 1934 type 801 (*1) check proof machine, available as well in a Sterling version (*2).

(803 in operation, taken from this blog)

Of course there were as well electronic LSD calculators. A great example might be the Anita Mark 10 which in addition could convert between LSD and decimal.

Were the underlying computations typically performed in terms of decimal fractions of pounds, in binary or decimal integer multiples of pence (or farthings!),

No, no Farthings and no Guineas (*3) either. Bookkeeping was only done in Pounds, Shillings and Pence. When recording of Farthings was required, they were done as fractional Pence, like 11¾p (*4). That's also the reason why the linked COBOL manual reminds users to take care of possible fractional pence - something that comes to be if Farthings are handled.

or by keeping track of pounds, shillings, and pence as binary or decimal integers?

Yes - all of them. In the end it depends as much on application as on hardware (and language runtime). Converting everything to pence and converting back for display and output purpose was as common as having three dedicated fields handled separat - or with some computers it was possible to handle a dedicated sterling data type, often a variant of the decimal (BCD) type but handling carry accordingly to LSD structure (*5). This includes modified micro programs for standard mainframes.

The most well known example with hardware operating on LSD might be 1960s ICT 1300 series.

(From Wikipedia)

Another interesting example is shown by the English Electric Deuce series:

(From Wikipedia *6)

While not operating directly on LSD, it could execute complex divisions and multiplications with insertion and removal of elements during operation, a feature that allowed conversion between LSD and Pence (and back) in a single assembly instruction. Somewhat similar to a PACK/UNPACK operation for converting EBCDIC or ASCII to BCD. In fact, that operation is so unusual that it might as well have been created especially for that purpose.

My research so far has only found one useful reference, and IBM System 360 Cobol specification that seems to say that computations were performed in pence and then output in pounds, shillings, and pence with a special formatting "PICTURE" See pages 117-118 at

Not sure. To me this reads as if done by using dedicated decimal field for each unit.

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*1 - No, that's not the 801 processor, the father of all RISC. IBM did reuse the number :))

*2 - Interesting side note, the follow up 803 was sold all the way until 1981 - about the time when even the slowest moving US bank would switch to digital handling

*3 - Guineas were as well not recorded as such, but as one pound and one shilling or 21 shillings (Equivalent to £1.05 in decimal notation).

*4 - 11 Pence and 3 Farthings was the Victorian equivalent of today's 9.95 pricing - a Farthing short of a Shilling to make it look less.

*5 - This is especially true with early 18/36 bit machines using 6 bit characters. Here BCD arithmetic was often done using one digit per 6 bit char, which directly corresponds how punch cards (the most common source for data) were read. This allowed to hold pence (0..11) as well as shilling (0..19) as a single 'BCD' digit - which in turn directly corresponds to the way the GB standard (BSI) encoding for Sterling on punch card was done. Nicely mentioned on p.114 of the linked document.

*6 - What a massive beauty - that's what a real computer has to look like :))

Answer 2

I started my first job programming in 1979, eight years after decimalization, at a major UK bank. I remember someone telling me that they did everything in pence because that was how it was done in LSD days

Answer 3

As you acknowledge in your question, IBM's implementation of COBOL had special PICTURE clauses to represent £sd. So did PL/I.

There is also a L suffix for pre-decimalisation British currency where the elements designate pounds, shillings and pence. This is converted into pence for storage.

TEST: PROCEDURE OPTIONS(MAIN);
  DECLARE AMT FIXED BINARY(16);
  AMT = 1.5.2L;
  PUT FILE (SCARDS) LIST(AMT);
END TEST;

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Another approach, which doesn't require having built-in language support, is to store monetary amounts as an integer multiple of the smallest unit. For modern decimal currency (Pound, Dollar, or Euro), this means 1/100ths, but for £sd you could just store pennies (1/240ths of a pound). (Or farthings (1/960th of a pound) if you wanted to handle historical calculations from before the farthing and halfpenny were discontinued.) In a modern programming language, this can be done with a class defining overloaded operators for arithmetic, and functions for formatting and conversions to/from decimal currency.

Answer 4

I was writing programs for small computers prior to decimalisation. No customers were interested in recording halfpennies or farthings in their accounting so just had to keep all the records in old pence internally. Just needed a conversion when displaying the final output in £sd, and of course on the keyboard input as well.

After decimalisation can remember that most customers had new pence as their base unit but a few wanted to take into account new halfpennies. They were nearly all persuaded out of it.

Answer 5

Decimalisation roughly overlapped with the era of computerisation.

The transition to decimalisation in the UK occurred in February 1971, but it had been on the cards since the early 60s. There was little commercial computerisation in the 50s, so anyone commissioning accounting software in the 60s always had some regard that decimalisation may be impending.

Before computers, banks used mechanical and electromechanical machines for accounting work. Since decimalisation meant these machines had to be physically revamped, many banks targeted some kind of computerisation of their operations by 1971 to avoid the cost and hassle of this overhaul (which would otherwise have had to be executed countrywide over a single long weekend).

The technical term for the LSD system is a "mixed radix" system, and performing arithmetic in such systems is simply about converting all values into multiples of the smallest unit, performing the arithmetic, then converting back into the mixed radix format. Integer division and remainder operators are the workhorses of this arithmetic.

There were 20 shillings to a pound, 12 pennies to a shilling, and therefore 240 pennies to a pound.

Converting say 270 pennies into £1/2s/6d for presentation is done like so:

Amt = 270
Ldiv = Amt / 240 (= 1)
Lrem = Amt % 240 (= 30)
Sdiv = Lrem / 12 (= 2)
Srem = Lrem % 12 (= 6)

The Ldiv, Sdiv, and Srem calculated values are then the amounts in LSD form.

The "LSD" abbreviation derives from Latin, in which Libra, Solidus, and Denarius are the words for Pound, Shilling, and Pence. The £ (pound) sign is a stylised L.

Historically there had also been halfpennies and farthings (fourth-ings, or quarters, of a penny), as well as further subdivisions in certain times and places. The farthing was withdrawn from the UK mainland in 1961, but the halfpenny survived decimalisation in 1971, not being withdrawn until 1984.

By working natively in pennies (or subdivisons thereof), the transition between LSD and decimal was a relatively simple case of changing the presentation of the native amount, as well as a one-time revaluation of all accounts on "decimal day" in 1971. Legislation determined exactly how the revaluation was to occur.

I'm led to believe that there are few if any extant bank computer systems which pre-date decimalisation, with any that did having been completely overhauled in the 70s or 80s at the latest.

But the answer to the question is that any computer system that traversed decimalisation, likely performed arithmetic natively in some fractions of a penny - which is an approach that works for both LSD and decimal, by simply tweaking the presentation of the native amount.

And any computer system dating from before the mid-80s and with software written bespoke in Britain and for Britain (when halfpennies were still in circulation) - and I believe these do still exist - is probably still capable internally of representing fractions of a penny.

Nowadays, new software is still likely to cope internally with decimal currency fractions smaller than a penny, not as a hangover from past British coinage, but simply as a flexible approach (including coping with accounting in foreign currencies).