You can look at my Measure script for what the API is capable of in that regard. You can't add new methods to the tool, but you can perform your own calculations given two (or more) points on the page. In that script, I'm measuring between tokens and using the configured formula, but you could imagine using your own (logarithmic distance or thresholds or whatever). You could also create a marker and drag it about providing a measurement on the page for its journey, etc.
