Then as you move the mouse around the x and y offsets distance and angle are displayed. That is a good start and I use the edge length setting in almost every project. Click and drag in the viewport to define the initial start and end point for the ruler.
Calculating distances between two points using geodesic paths By Bart on March 3 2016 Add-ons Patmo141 is working on a Python script to calculate distances on object meshes so actually following the surface.
The measure tool can measure the distance from the cursor to the selected object so just play with the SHIFT S menu to align the cursor to whatever you need but it will be object center. Once you select a vertex it will tell you the coordinates of the vertex. I am an artist working with a python software developer. To accurately measure in Blender while in edit mode go to the overlay menu in the top right corner.