Often, when designing a part or assembly, there are certain dimensions that I know confidently.  However, there are often other dimensions that I do not yet know or do not know well.  Rather than stop all progress until I have that information, I'll simply put in something reasonable - an estimate - and continue. 

I'd like to know if there is any way to tag or mark these dimensions as estimates so that I don't use them later for designing something critical until I've got the difinitive dimension.  Something akin to "tainted" data in programming?