I wrote an App to measure Any graphic for which only one dimension is known. The graphic can be an STL
The primary purpose at the time was to measure electronic parts but, it works for any graphic or 'whatever' on your monitor.
Example of using it in Simplify, below... CLICK on the video to open/view it
• Loaded the .STL into Simplify
• I know the width of the Part (see drawing image)
• Though also knowing the Dia of the large hole, the attached video shows using the App to confirm the Dia...
(I did not fuss with trying to get an exact dimension...)
The app is written in Java and requires Java8 (JRE 1.8) as minimum.
The app with use info is posted here