A..HA! Father Steve, you have hit on the very thing: no one would use imprecise indicators where exact measurement is vital. I've seen many a recipe with, for ex., a "pinch" of salt listed in the ingredients. A few grains more or less of that isn't going to make a noticeable difference. But an extra grain of something very potent might. I would not want my pharmacist to make up capsules for me according to what a "pinch" is!
Some years ago I read that developers of cake mixes cook them up with instructions and ingredients that depart further and further from what they should be, until it gets to the point where the cake just...won't. They do this so as to be able to allow for a wide margin of error that they know will occur when customers get hold of them.