This may have been mentioned before but just in case … …

Window and door openings, I run a suitably coloured felt tip alomg the edge, however the hands not being as steady as they uster was, I would sometimes slip and mark the surrounding brick, stone or tile, I now do it from the reverse side before fitting windows and doors, you see what I mean about the unsteady hand!

For us folks over 70, that's a great hint.  Thanks

A useful tip, Mike.

I have also used crayons and weathering chalks for the same purposes - easier to wipe off slip ups!