In recent years, I have taken up collecting old books, and in reading them I am coming to be aware, more than I already was, that we "don't know that we are born".
Here's an as yet poorly developed example...
Until modern times, in the UK, the basic unit of currency was the pound. It was divided into twenty shillings, and each of them was divided into twelve pennies.
Fine, most of the time. No big deal.
But what happens if you want to know how much 127 copies of a book cost, if one of them is 3 pounds, 19 shillings and 11 pence... the old equivalent (which we rarely met in those less tedious times) of £3.99 in modern terms.
Not too hard for you? Okay, then... what's 17% of £523 pounds, 8 shillings and 9 pence?
Remember: There were no calculators, let alone computers.
To meet the need, enterprising folk put out "ready reckoners"....
The one in the illustration was nicely "pocket" sized.
(My thanks to Tim and Pinda Bryars, book and map sellers, Cecil Court, London, for access to the copy I am illustrating this with. Note that the photos have been massaged in PhotoPlus, to compensate for some carelessness in my photography. They should not be taken as accurate representations of the book, should you wish to purchase Tim's copy.)
On the left, a double page from the book... almost all of it was taken up by page after page of this sort of stuff.
On the right, a close-up of a bit of what is shown above. With it, you can tell me what 101 times 6 shillings and one pence comes to, can't you? ("6 shillings, one pence" would usually be written "6/1" in the days when the units were in use.)
I worked it out by hand, with a calculator for things like "606 divided by 20", in a mere 64 seconds. (Answer at the bottom, in case you aren't sure of yours.)
Why does the page have "72d" in the top margin? (That was how 72 "pence" was written. Pounds were abbreviated "L"... making "pounds/shilling/pence", abbreviated, "L/s/d". Perhaps not a coincidence? How else did "they" come up with 12 pennies in a shilling, 20 shillings in a pound?
I have, by the way, only given you the highlights of the monetary system. There was a "half crown" coin, worth "two and six", i.e. two shillings and sixpence. But, in everyday circulation, no "crown" coin. There were guineas... in theory. A nice suit might cost "fifty guineas"... Fifty pounds and fifty shillings, but it wouldn't be expressed thus, there was no guinea coin, and you couldn't write a cheque in guineas. You "just knew" to make the cheque out for fifty two pounds, ten shillings.
Ironic, really. Just about as computers came in and the eccentric monetary system would have been neither here nor there, the old ways were abandoned.
But perhaps, in some ways, it was just as well. One less of the "treats" of the "good old days" that modern folk don't have to deal with.
(101) times (6 shillings, one pence) is 30 pounds, 14 shillings, 5 pence, as I'm sure you worked out for yourself, both by hand and by "Ready Reckoner". And 73d is just another way of saying "6/1".
For more stuff about collector's books and maps, maybe try Book (and map) Mad, but the page you are reading is "officially" part of The Flat Earth Academy, which tries to offer some of the things that some schools used to offer, and some no longer do.
I can't think why you would want to, but, just in case you do want to contact the editor of this page, the link will tell you how.