3 different Letterspacing setups using two masters

Here’s one thing I’d love to know how to do…
Have the middle weight (regular/medium) a certain letterspacing - comfortable for reading point sizes, and the extremes - extraLight, Black letterspaced for display

Doesn’t sound mathematically possible to me.

I suppose a custom parameter could be added to Glyphs that would allow users to add tracking (if one doesn’t already exist). But you would still have to fix the final spacing of intermediate fonts manually, and you’ll need an intermediate master to interpolate between extra light and black anyway.

Do you always use an extra middle master apart from Light/Black? Does it enter your design in the beginning of the design process or later? I’ve had good results only using 2 masters, but I did use 3 masters before Georg advised me it would be simpler to use just 2.

One generally must. Light fonts have almost no contrast and black font have tremendous contrast, so it is hard to interpolate some useful between them. And there are the aforementioned spacing problems.

As for when to design the middle, that really is up to you. Some designers prefer to start in the middle and work out, others start with the extremes and then just clean up intermediate masters.

It depends on how black your black is. I usually have no middle master. There are some glyphs that need some special adjustments but that can be handled with the the bracket trick.