I usually just hook up my reg. set to the tank. and do a reading, like drifter said make sure to purge the air from 2nd stage before disconnecting, I thought about buying the simple gauge but when i saw the price i said ill wait on this. Watchout in asking santa for a drysuit, if he feels you haveny been a good girl you just might end up with a red santa suit! Non-Insulated. All the dive shops that ive been to dont purge the tank, if its half full, they fill the empty half and no matter how much goes in you pay for a full fill, and since i dont dive dry, I fill my tanks for winter storage then in the spring I dump the air then have em re-filled