1. This rule was designed for business use with pre-decimal
currency in Britain. (Before 1971 the unit of currency was the pound sterling divided in
20 shillings each of which was divided into 12 pence).
2. The rule has CF and DF scales folded at 3.6, rather than 3.14. However having scales
being folded at 3.6 is common for commercial rules. For some reason interest was usually
based on 360 days per year.
3. The cursor has a hair line to conveniently multiply by 365 rather 360 but only on the
4. The rule has gauge points at 12 and 144.
5. The rule has log-log scales, for compound interest calculations, on the reverse of the
slide. It is necessary to remove and reverse the slide to use these scales. On most rules
the log-log scales are on the stock.
6. On the bottom edge the rule has a scale for converting shillings and pence to decimals
fractions of a pound.
7. Among the conversions on the back are some rather unusual Russian units (Arschins and
Tschetwerts for example).