Rolf,
I have been using inexpensive digital scales a long time. But I always keep 2 or 3 on hand so I will always have a back up. Same thing with vacuum pumps. Half way into a big lay up job is no time for either item to quit on you.

I mix batches anywhere from 100g to 3kg and find scales with a 1g accuracy (or is the word precision) do fine. The specification on a typical bulk epoxy resin (Dow Chemical DER 330) has the epoxide equivilent weight between 176 and 183. It is this property that determines the number of cross linking sites available for a given curing agent. Curing agents too have variability in their amine weight. So, even you have a super accurate scale, what you are mixing has some variability and that dosen't do much good.