There are two scales mentioned early on in the "Mixing by Weight"
thread. I don't remember what they're called but there's "the one from eBay" and "the one from Amazon." I have the eBay one (seller: anyvolume) and it doesn't have an auto-shutoff (I've left it for upwards of 30 minutes and it was still on, on battery power.) It
does have the auto-zeroing "feature (not a bug)" that can miss drops after a tare, if you add them one at a time. This is annoying but not disastrously so, you just have to be aware of it and not let it settle between individual drops until a weight other than 0.00 is registered. If you
need to add by just a few drops, but just counting them isn't good enough (e.g. you need .05% of something and don't know if that's 2 drops or 3), then put a bottle cap or something to tip the scale off 0.00 and then subtract the difference.