[whpalmer4]

I asked Bill Van Hecke about something very similar to this at Macworld last week. His suggestion was:

1. Set up desired scale and grid with Canvas:Size and Canvas:Grid inspectors
2. Draw a straight line, holding the shift key to align with the grid
3. Option-double-click on the line to add a label (might be different depending on your Tool Preferences settings)
4. Edit->Insert Variable->Line Length
5. Bring up the Properties:Geometry inspector and adjust the various label parameters to suit
6. Drag the newly created line over to the side of the diagram and duplicate as needed (or create a stencil, I suppose)
7. Use the knob in the Properties:Geometry inspector when you need a line at a different angle.

One thing I've noticed is that label sizes don't get rescaled if you change the scale of the document. I don't see an easy way to redo a bunch of labels at once, so it's probably worth getting that nailed down before you do much drawing, or you might have microscopic or gigantic labels!