I add the weight of the bar except for when i use the Smith machine, cause i am never sure home much the bar weighs. Plus, i think it doesn't matter so long as you are consistent. Its about progress, not the weight itself.
I usuallly assume that the eZbar is 15 and the barbell is 45. So long as i use the same bar every time, it don't matter if those are accurate.
-Fatty