A method of expressing a sum of money as a decimal of a £ to 3 places has long been known. When further decimals are necessary, they may be got by the following simple rule, which appears to be new: multiply the last two decimals found at any stage of the process (after the first 3 have been obtained) by 4, take the digit in the ten's place of the product, append it to the decimals already found as the next decimal, and repeat the process; with the proviso that should the 4-product end with 48, 68, or 88 the digit in the ten's place is to be taken as 5, 7, or 9 respectively.