I would suggest just buying one of those small digital scales from e-bay for like, 10 bucks.

I know that nothing beats the feeling when you think that your dealing is trying to fuck you, and you pull out that scale, you weight it out, and find that it's 1.5 grams under what it's supposed to be, and every time after that, they make sure that they give you the correct amount. I should know, I've done it before, and it's definately worth it.