Another way of doing it is to not comment at all.
(Sorry, I could not be bothered to find the shocked face icon!)
The reasoning is as follows: An inaccurate comment is more dangerous than no comment at all, as developers will read the comment and then not read the code to confirm it is true.
Comments need to be kept up to date as much as any other documentation and sometimes they don't get kept up to date with the code.
The fix for this is to write the code in such a way that the code is self-documenting, so if you need code that gets the mean sales figures for the previous three months you have a function/view/procedure called Previous3MonthsSales. If you have a block of code in a procedure that is hard to understand then take it out into it's own procedure and name the new procedure accordingly.
The only discipline you then have is to ensure your objects only do what they say they do and nothing else, and they do it right! If someone wants Previous3MonthsSales changed to 4 months then create a new code object to do that and name it Previous4MonthsSales.
Just an alternative view...