Pence / Penny / Shilling / Farthing

Easy. The whole system is based on the pound having 240 pence.

12 Pence make a Shilling. 20 Shillings make a Pound.

Coins issued were:
Farthing (Quarter of a Penny) 4:1 Penny
Half Penny 2:1
Penny

As I have said, 12 Pennies make a Shilling:
Two Pence ("Tuppence") 6:1 Shilling
Three Pence ("Thruppence" or "Three Penny Bit") 4:1 Shilling
Four Pence ("Groat") 3:1 Shilling
Six Pence ("Tanner") 2:1 Shilling
Shilling ("Bob")

Twenty Shillings make a Pound:
Florin - Two Shillings - 10:1 Pound
Half Crown - Two Shillings, Six Pence [i.e., two and a half shillings] 8:1 Pound
Crown - Five Shillings 4:1 Pound

What it's hard to wrap your mind around is that everything is a base 12, because we're used to decimals and their nice round numbers based on tens to make 100's...

What confuses things further is that when Britain finally "went decimal" in 1971, they changed from "240 old pence to the pound", to "100 new pence to the pound". They kept the pound unit exactly the same. Thus, the old shilling became equal to 5 new pence, and so forth. In 1983, they dropped the word "new" from the coins, making the currency system of Britain today 100 pence to the pound.

Apart from the dates, it's usually easy to tell the coins from the two systems apart: "new pence" are in normal decimal multiples (1,2,5,10,20,50 pence) while "old pence" are in strange numbers (3, 6 pence). The only unit that causes problems are the pennies and halfpennies. "Large" ones are predecimal, "small" ones are decimal.

http://en.wikipedia.org/wiki/Denarius .
http://en.wikipedia.org/wiki/Sceat
http://en.wikipedia.org/wiki/Penny
http://en.wikipedia.org/wiki/Pennyweight
http://en.wikipedia.org/wiki/Pound_sterling
http://www.telegraph.co.uk/news/139...terling.html
Its a long history.
Just ask Sap and all other expert here in the forum.