I don't have an calibration weight so what can i use to calibrate my scale? or to find how accurate it is?
Use a new nickel, if you're in the US that is. They have a mass of exactly 5 grams. (dunno what the mass tolerance is though)
Yeah, that's just fine. Also, it might weigh less if it's slightly worn. And again, since the coins are a mass produced product, they all have some tolerance on mass, but I don't know what it is.