Painting grades with a paint marker that can be brushed away

Painting names makes it easier to find the Route or Boulder you are looking for but if you do not have a topo, the grade is even more important. The problem is of course that the grade can be changed and that it is kind of hard using a paint brush. With the paint marker in the picture, it is super easy to paint grades on the rock and if the grade changes, you can brush it away with some water within a minute, at least on granite.