Create routes when the measure source is not "length"?

I need to do some linear referencing work with a network of lines with specific beginning and endpoints. The first step is to take the network of lines and use the geoprocessing tool “Create Routes” in the linear referencing toolbox. This much I know.

However, I am unable to find anything online about how to create routes with a from-measure field and a to-measure field where the measure source is “Values from two fields”. Every example online seems to use “length” and the ArcGIS help is not very helpful. If I have point features on the endpoints of my lines, is there a way to use those points to populate fields I can use as from- measure field and to-measure field? Apparently these fields have to be numeric, but honestly I do not know what kind of “numeric” values I need. Has anyone done this before?