THANKS........I JUST BOUGHT MYSELF A TIRE GAUGE.......I'LL HAVE TO PLAY WITH IT & SEE HOW IT GOES......ARE THOSE VALVE STEM AUTOMATIC AIR DOWN THINGYS ANY GOOD ÂÂ
 WHERE DID I SEE THEM  HMMMMM....... I CAN'T REMEMBER...ANY ONE KNOW  :-/  .........  THANKS  MATTY   
Use the air gage. Some air gages come with a nipple on the head. Or just push the scale back in and use that. You don't want to let out a lot of air at once. You want to gradually go down over a week or more period. Do remember that in hotter ambient temps, the air pressure will rise.
As for those auto air downs, check out Klune V's web site. I wouldn't get those anyways. They regulate the air pressure out only. Never understood why anyone would want those. Airing down as you drive to the trail? Sounds like a recipe of loss of control.....
I have a set of screw on bleeders. Typically same thing in design and application, but just a continous air down. I use these at the trail head to air down if I don't have a valve stem wrench (vsw). You'll be getting out at the trail head anyhow to lock in hubs, check air pressure, maybe adjust shock valving, securing interior items, getting cold water ready, getting something to eat, changing of clothing, taking top down, etc. many reasons, maybe even a driver's meeting if you are with a large group.
The vsw is a cap that has a finger on it. The finger is split to be able to totally remove the valve out of the stem. This is rapid air down at it's best. With a large tire, just pull the valve till you start to hear a whistle. Then measure pressure and it should be near 12 psi. The wrench is readily available at any auto parts section of any store. Usually where you find the plastic stem caps and stems and valves. Usually 4 for under $1.