OP
We'll cover this in class, but the single most common problem is the diver's inability to hold their compass on their lubber line. Back when compasses were first put on sail boats, most sailors could navigate with them except for the "idiots" which they affectionately called "lubbers". So they added a line on the compass to indicate the center line (direction) of the boat, which they then dubbed the idiot line, or Lubber Line in their venacular. For a diver, this line is still not "lubber proof": you have to center it and keep it level enough to keep working. Next time you hear someone say "land lubber", you'll know just where that word came from: idiots who don't have their sea legs yet! 
So as you use your compass, remember to center it on the idiot holding the compass. It's not unusual to hear my students giggling as they play with the compass.
So as you use your compass, remember to center it on the idiot holding the compass. It's not unusual to hear my students giggling as they play with the compass.Fully extended? Not needed. Centered and aligned with the diver? Essential. Unless the console has a really long hose, it's going to be canted left to right. Unless your arms are alien in dimension, keeping the compass on your wrist will cant the compass from right to left on your left wrist and left to right on your right wrist. The compass' Lubber Line must align with the Lubber holding the compass. I hope that answers the question.
