Approach help for a scanning tunneling microscope, or really any scanning probe microscope. I don’t think I have posted this one yet. Again, this diagram may straddle the boundary between useful and dumb.
When a scanning probe microscope approaches a surface, there is often a two-stage approach system. The scanning unit can extend the tip some distance L in an attempt to reach the surface. If the surface is not found, then a coarse approach unit can advance a step of distance M, which is less than L. This process continues until the surface is found.
In case you are wondering, I do have a normal process flow-type diagram (what are those normally called?) for this process as well. I can post it tomorrow.