StemAnalyzer is a RoboFont extension for setting PostScript stemSnap values in a UFO.
To use the extension, select the glyphs you want to analyze and click Analyze Selected Glyphs. This will populate the text fields below, you can then set the values into your font's postscriptStemSnapH and postscriptStemSnapV.
You can also view the stem values in the glyphWindow for each analyzed glyph.
This extension was originally written by Jérémie Hornus and was updated for RoboFont 4 by Connor Davenport. All the math has stayed the same, only updates are to the UI and drawing methods.