The Average Calculator (AvgCalc) is a tool for calculating a rolling average. One can continue to enter values, which will calculate the average of all entered values thus far.
Future Value (FutVal) is a tool for calculating interest. It takes an initial value, a percentage and a number of years, and will figure out the interest gained and give you the new sum of money.
This tool can be used to find a percentage of the Value-Added Tax on a purchase. It then provides the amount of money that should be charged VAT and the amount of money that should not be charged. This can be used in accounting software if you need to claim back a certain amount of VAT from HMRC, if you can't claim 100% of it.