Mateusz Pusz

Please note that `isq::height` can be negative. Probably, you are abusing `isq::width` for your coordinate needs. Width is something that you may measure with a caliper. There is no physical...

I would do something like: ```cpp QUANTITY_SPEC(pos_x, isq::length); QUANTITY_SPEC(pos_y, isq::length); QUANTITY_SPEC(pos_z, isq::length); ```

> If it's constrained, the only reasonable way to change width values is to work on lengths before converting to widths. Yes, if we really want to subtract two widths...

>I think it's perfectly valid for a difference of widths to be negative. The ISQ defines width as: > minimum length of a straight line segment between two parallel straight...

> But widths don't have inverse elements, so it doesn't form a vector space. It's still useful to have width vectors, and have their magnitude result in an actual width....

Now, let's come back to vectors. If we deal with vectors, we should use `isq::position_vector` (if our vector originates from the center of the coordinate system and expresses a point/position)...

OK, I was confused because you mentioned taking the magnitude of a vector several times. What does the magnitude of such a vector/difference quantity mean?

Also, I think I was wrong in claiming that a negative width has no physical sense. For example, let's assume that we measure the width of brake pads in my...

Does it mean that in case we will add support for non-negative quantities they should actually apply only to the values in the `quantity_point` and not for `quantity`?

> If quantity represents a vector, then it can't represent negative quantities like width. But you can indeed represent changes in width. Like you mention with https://github.com/mpusz/mp-units/issues/468#issuecomment-1708157645. That's what vectors...