Yep, DMM = digital multi meter. You'll be measuring the resistance in ohms on your meter. I asked awhile back what an appropriate setting should be on the laser and everyone seemed to think I was crazy
They said that all of them will be different and that you'll just have to do trial and error. Mark your original spot and slightly turn the pot. Test it out, then repeat as necessary.
I'd suggest getting a reading off of a laser you have that works, then use that as a possible base for the other non working laser. I would assume there is a range that the laser should be in, but I don't think anyone here knows...
EDIT: I just tweaked a laser I thought was bad to 545 and it's working fine now. Another laser that works 100% is at 549. Again, not sure if you'll find the ratings of any use, but for me it's working.