As noted above, the closer you can get to the size you require, the more likely you are to get acurate results...

One thing not discussed is LARGE quantities...

I have a 1 gallon jug that I remarked very accurately with a scratch into the side and marker embedded into it. I found it in the automotive section or a local hardware store and has a 2 part lid that opens up to avoid splashing... I think it's for mixing antifreeze or something like that. I use it for Dektol, Hypo clear etc... Anything that needs to be made up to 1 Gallon quantities.

Hope that helps,

joe