Business tools

Margin and markup, VAT, a discount that has to land on a round number, the instalment on a loan, how many working days sit between two dates, what time a call falls in for the other side of the world. These are the arithmetic tasks people rebuild in a spreadsheet every few weeks and get subtly wrong, margin confused with markup being the classic. The margin calculator, the loan calculator and the time zone converter each do one of them properly, and remember nothing about you.