We just put the right cvts in the right places, but we have to put them there at all. Then we can override at what size a 1 pixel stem becomes 2 pixels. We can also override whether e.g. the round strokes should be tied to the straight ones or vice versa for more contrast at smaller sizes. Outlines may have been scanned in from hand-drawings. Outlines may have been converted from other outline formats.
Straight lines are still a problem.
For example, going from Type 1 to TrueType, the conversion must scale from a 1000 by 1000 grid to a 2048 by 2048 grid. The problem is the division, again. We'll use average stroke weight for actual cvt value. The O looks fairy straightforward to do. Cvts for height guidelines are a bit tricky.