Working with a non-decimal system can be problematic and confusing. This might be the case when one tries to study financial topics during the early 18th century. In those days, a English pound was divided into 20 shillings, and each shilling numbered 12 pence.
Two tools were created to ease working with this non-decimal system. One is designed to convert a daily payment into its yearly equivalent. In documents on, for example, half-pay officers, the sums paid to these officers is given in daily or yearly sums. The second tool is a simple calculator, to enable addition and subtraction.
The tools can be found at http://drenthpublishing.nl/research.html.