Another excuse for more failures:-)

My father worked in a bank, and showed me the tricks they used.

There were 960 farthings in a pound - almost 1000 - so by converting everything to farthings it was nearly decimal pounds and the last decimal place was adjusted by adding up to three hundredths of a pound. The break points where each number applied were simply memorised.

This allowed rapid conversion to and from decimal currencies without the use either of log tables or a slide rule or a calculator.

Stuff and nonsense. People did it every day with no trouble whatever.

The wonderful HP35. It became available when we were looking, at work, for a second "four function" laptop sized Canon with a budget of about £1k (nearly a year's salary for a new graduate). The salesman had the shortest sales pitch ever. "Here it is, then". We'd all read up on RPN so didn't need any instruction; we ordered three on the spot for, iirc, £1k total.

I never met a teacher who, or textbook which, propounded the reduction?expansion method as the norm for compound unit arithmetic done manually.

I remember a couple of lessons were we were taught how to use log tables in the early 80s, but I don't recall actually needing to take a book of tables into any exam (although calculators were required for maths and physics though).

There may have been a question on reading tables with an except of a table reproduced in the paper I suppose - but can't remember for sure.

In the 19th century the National Debt Office just converted all sums into decimal pounds and used them for all its internal workings and books.

Probably getting on for £800 worth today then!

The first one I remember having use of was a 4 function Prinzetronic[1] that cost about £20 in the late 70s (so probably ~£120 in today's money)

Or, go multiply and forth!

No, because it wasn't necessary. Adding up sums of old money was an easy task. People today are just imagining that it must have been difficult because

Our school had exam copies of Log Tables. They didn't have notes on the blank bits.

The "pence" I was referring to *was* the 240 to the pound variety...

Just the basic four arithmetic functions. Not even square roots. I don't know whether there were any scientific calculators in 1971.

On 10/02/2022 11:38, Robin wrote: ...

Is that related to the introduction of the florin in 1849?

I now have an HP-25 application on my phone.

AFAIK not directly. The NDO just converted to pounds to 3 decimal places. But I don't doubt it was in the wider context of all the interest around then in decimalisation of the currency that led to the florin.

Robin finds walking upright difficult and complicated.

After further creaking and rattling from what increasingly feels like a mechanical brain (with some very loose cogs), I think the NDO system was more closely related to the florin in that its decimal unit was not the pound but 1/10th of a pound. Probably. It's a long time since one GH prompted me to read the reports from the 1860s.

I suspect it is not necessarily a case that they can't do it, as more a case of unless you are familiar with working in a mixed number base systems and are familiar with the day to day tricks and rules of thumb to ease the process, the "obvious" solution is to reduce all the values to the lowest common denominator and work there.

Now for adding and subtracting, in reality it is not that difficult to work in the various number bases, and adjust the base when carrying or borrowing from one "column" to the other. It gets much harder when doing division (to my mind at least - but then I have never used LSD in real life!)

For those who did it frequently. Mother used to keep the accounts for the family and would tot up in her head as she ran her fingers down the page. After decimalisation, and after she becam accustomed to the 'new way' she commented how much easier it was 'now'. Her mathematical prowess on cash books was one thing that did not succumb to her late life dementia.

Hmm.