Most coherent, developed, tested materials
Overview of measuring distances -- Dr. Luisa Rebull (2020) but developed over 10 years
Somewhat less coherent (or less standalone) materials
Measuring distances in IRSA tools - Click on the ruler icon, then click and drag in the image to measure a distance. Click on the layers icon to bring up a pop-up that specifies the units for the length of the vector you have drawn in degrees, arcminutes, or arcseconds.