I apologize. I know where my thinking went wrong now (see next paragraph). But just theoretically – Actually, it would be the same type calculator. The user would enter the qty of ml to make and the calculator would do the allocations using the weights of the ingredients, keeping the final volume constant, allowing the final weight to float.
It’s a moot point, really. I think I was just confused about why we measure using weights. I just started mixing a few months ago, and started mixing by weight recently. I see that it makes more sense to mix by volume, but using drops is terribly imprecise, and trying to measure using graduated cylinders and eyeballs is inconvenient and also a bit imprecise. But if you know how much the volume you want should weigh, you can just add ingredients one at a time to one, final container on a scale and, depending on the precision of the scale (and your pouring hand), you should be able to be fairly precise. So I guess I answered my own original question.