Hello everyone,
Just an open question I had. What are the pros and cons of drawing a typeface based on a 1000 upm grid, 2000 or even 2048?
Depending on the typeface I’m working on I use 1000 upm or 2000 upm but never 2048. But I saw that some people do.
See this TypeDrawers thread for some in-depth notes on the topic: Units per em — TypeDrawers
At a high level, it really shouldn’t matter much in this day and age. Personally I only go above 1000UPM if the design calls for it. Microsoft recommends a UPM value for TTF files that is a power of 2, but I think it’s safe to ignore this guidance 
FYI, the Glyphs custom parameter description of the UPM:
…The value specified is the amount of units that will be used for the font size. A smaller value will cause the font to appear larger on screen, and vice versa. …
The ‘appear larger on screen’ seem to be wrong.
That is not wrong. It means if you just change that value, and don’t scale the rest of the font, The apparent font size will change. That is a good way to adjust the rendering size (e.g. to match it to other fonts).
Thanks. My testing code is wrong. You are right. 