Making guide lines lie on planes, edges, etc?

All of a sudden I’m having problems placing guidelines on surfaces in order to precisely locate lines or rectangles to make cuts or openings. The lines and points often lie slightly outside the plane or edge of the element I’m working with.

Is there a way to make the guides lie on a surface to line? Making the surface or line active doesn’t seem to work.

Using Sketchup Pro 2018 with Mac Mojave.

Maybe your surfaces are slightly off axes and Tape Measure Tool (which I assume you’re using) tries to snap to a global/ local axis instead of existing geometry?

Another thing I’m thinking of is model scale. Make sure you’re not modelling very small stuff, like fraction of a milimeter. This would create numerous artifacts of even prevent geometry from creating. If you want to create something very small, work in meters and scale your geometry down 100x or even 1000x only when you finish.

Thanks. I’m now ‘pulling’ guides off the axes to ensure accuracy.

They should be able to lock on a point, edge, intersection or plane and you can force the guide orientation with the arrow keys.