nano, you haven't specified any of the design brief you have to work to so anything I say must be a guess... If you are required to work in decimal, the most common method of representing numbers in most commercial calculators is some form of BinaryCodedDecimal - four bits represent 0-9, you store two decimal numbers per byte, and perform your calculations in decimal, just like you do with pen and paper. It isn't as fast as true binary maths, but you don't have to do any conversions for input or display, and any micro will do the BCD calculations far faster than any human can. Many types of calculations are faster done by using look up tables and interpolation rather than complex algorithms. I suggest you go and search for vintage calculator sites, particularly TI and HP. They often have details about how commercial calculators worked internally. I've seen some very detailed info including old patents on calculation methods used in famous historical calculators. Try some of the vintage calculator forums, some guys there know a lot about calculation methods. Good luck, Colin