I realize this is a very basic question, but however I can't find any basic Q&A on something so simple. I added three new points to a shapebatch in ArcMap. By default when I added them, it made the M-Value the equivalent of a minimum double value (-1.79769313486232E+308). I know this because I've written software to read ShapeFiles. For testing purposes I need to be able to change the M-values of these points to see how it handles certain values.
I've tried opening the 'Edit Sketch Properties' windows. It's grayed out and doesn't even contain an M column. All tutorials/guides I've come across pertain to PolyLineZ.
Is the M-value computed on something within the shapefile?