Oh that's weird I was about to put a set up in the classes!
But learn from my mistake, I'm putting these in the classies because they only mix up to 200 mls (well, 200g). Not the end of the world because you can hit tare and go again, but if you are regularly going for more than 200mls it will get old fast!
Scales you can't go far wrong, you want jewellery or coffee scales that do at least to 0.1g and hold the weight of the bottle toy are trying to make up - so a 500ml bottle will need a scale to 500g
Got my new ones coming today from Amazon for £8.