Measure/guide tool... How do I choose between a perpendicular guide and in-line guide?

It seems maddeningly random. I want to create a guide line that is perpendicular to the direction of the cursor, or straight in line with the movement of the cursor. I was hoping that simply using the ctrl key to add a plus sign next to the cursor would select for one or the other but it seems to do nothing.

I’m sorry that I have not yet learned how to upload a vid of the behavior. I hope that I’ve described it in sufficient detail.

There are three variations:

  • if you click on an edge and then move the cursor away, SketchUp will create a guide line parallel to that edge. Either click and drag or click, move, click will work, though I prefer the latter. You can type a specific offset distance from the edge. The usual arrow keys can be used to constrain the direction of the offset.
  • If you click on an endpoint the move the cursor, you can create a guide point with a “tail” leading from the guide back to the start point.
  • If you click on an endpoint, move the cursor, then click on a second endpoint, the tool will create a guide line that passes through those two points.

Guides are created with the tape measure tool, toggling the plus sign with control or option key on mac dictates wether a guide is being created (+) or if you are just using the tape measure to check a dimension and don’t want a guide placed (no+).

As I was typing @slbaumgartner laid out very nicely the way guides differ depending on if they are started mid-edge or at a node or point. Here is an example of the different methods being used.