When I first started, I would measure out a few batches, for example 3 cups of resin and 3 cups of hardener. But I would only mix them as I needed them, so I'd mix the first batch and pour that into my pot and start the infusion. If it started running low I could quickly mix the next batch and pour it in, no stress. Then if I ended up with more than I needed, I hadn't mixed it yet so I could pour it back into the containers. Obviously had a couple of grams wastage from what I couldn't get out of the cup, so it's not ideal but it was a good way of getting a feel for how much resin I needed without the stress of realising I wasn't going to have enough and measuring some more.