I own the one you bought. I like it a lot. The dots are springloaden little stoppers sunken in the baseboard. You can twist them with a little screwdriver and make them jump up some 3 millimeter to act as stoppers for the papersize you use. Sometimes you may have to replace "lame"springs with ballpointsprings depending on the age of your board. The symbols are designed to quickly adjust the arms to the papersize you use. Papersizes from different manufacturers are not always equal so I made my own markings as I did on my enlargercollumn. I hope the gasspring on your board is stil under enough pressure. I had to replace mine some time ago. They can be ordered from Dunco. Congratulations, it's a good board. You will never want another....

Jaap Jan