An RCBS 5-10 beam scale. I weigh out loads at home and carry a bunch of vials marked with masking tape when working up a "most accurate" load.
Alternatively, I use a measure and then throw 10 charges to see what it really throws by measuring it. I've found NO calibrated measures that throw what they are marked at with either 2Fg or 3Fg. (The T/C ones I have are within 5%, I have an Italian measure that is off 27%!! That's enough to be potentially dangerous if you load hot). I keep a list of what my measures truly throw, and that is where I come up with the weights I post.
My two favorite and most used turkey-bone measures happen to throw those charges. If I lose one I'll know exactly what to make the replacement to hold. When I make measures I work them to even numbers, in increments of two grains, because THAT is as accurate as I think a body can measure in the field.
So . . . does 1 grain make a real difference; say 85 vs. 84 gr? IMHO not enough that you'd ever notice. I just don't happen to have an 85 gr measure. :haha: You'll also see me mention a 42 gr squirrel charge for my .54. That, by cosmic chance, happens to be what a .45 Long Colt case holds if filled to the mouth with 2Fg. :winking: And a double charge with that happens to be . . . SHAZAM! . . . 84 gr. And, my sliding T/C brass measure throws 84 gr at the third click instead of 80 as expected. :hmm:
So, you see, it's not because I am precise. It's because I am somewhat lazy and happen to have measures in those volumes.