Question about the 3px jump in my variable font when the weight hits 640 | Crafting With Code

Derek Walker · 2026-10-17T21:05:04.343185+00:00

So I spent most of last weekend chasing this stupid 3px baseline jump in a variable font I'm building, and it took me 9 hours to track down something that should've taken 20 minutes. Every time the weight axis crossed 640, my lowercase m and n would shift up just a hair. I tried redoing the masters in Glyphs, I checked my interpolation curves twice, I even rebuilt the whole thing in FontForge at 1am thinking it was a rounding issue. Turns out the culprit was one single off-curve point on the n that I'd dragged about 4 units off the axis by accident, and it threw off the whole blend. I only caught it because I ran a diff on the master coordinates and saw one value that didn't line up with its neighbor. Nine hours, folks, and the fix was moving one point back where it belonged. Has anyone else had a tiny point offset wreck a whole variable font like this, and is there a script that flags off-axis points so I don't lose another weekend?

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Question about the 3px jump in my variable font when the weight hits 640 | Crafting With Code - The Design Community Hub