SigFig is an Excel add-in.
At the heart of SigFig is an algorithm that determines the exact digital (base 10) representation of any double precision (8 byte) number. Endowed with this capability, SigFig has been configured to do a variety of things:
(1) It displays numbers in engineering format, with powers of 10 as multiples of 3.
(2) It gives various digit grouping options. For example, 1.234567 can be depicted as 1. 234 567.
(3) It can round numbers off to between 3 and 17 significant figures. Note that 17 significant figures is required to uniquely identify a specific double precision value.
(4) It promotes, but does not require, the practice of entering numbers as character strings (with an essentially unlimited number of significant figures); replacing Excel number entries which are limited to 15 significant figures).
(5) It promotes, but does not require, the practice of calculations being done in such a way that double precision is maintained in a chain of calculations. Excel arithmetics can lose precision in a variety of contexts, whereas Visual Basic arithmetics in the form of Excel user functions are much more reliable. Therefore, SigFig is shipped with a variety of arithmetic user functions that can be called out in your spreadsheet that operate on either (a) numbers or (b) numbers entered as character strings, and return numbers coded as character strings. Primary among these functions is RPN(), which is a reverse polish notation calculator, which implements the vast majority of functions you are likely to find on a scientific calculator.