> It really is just that the decimal system is what you are used to.

yeahright. So what's 17 and a half percent of 15 guineas 18 shillings and sevenpence three-farthings?

The problem with that monetary system is not that it wsn't base ten; it's that it wasn't base anything consistent.

Four farthings to the penny.
Twelve pence to the shilling.
Twenty shillings to the pound.

And that's not even counting things like crowns (five shillings) or guineas (one pound and one shilling). If you'd had thirteen pence to the shilling and thirteen shillings to the pound and scrapped those silly crowns and guineas and learned your times tables in base thirteen you'd shake your head in wonder at how anyone could work in something as silly as base ten.