Pencil tire gauges nowadays are junk. A little moisture in them from the tire,,,,,, ( say they were installed on a humid day, the water in the air gets sucked into the compressor, then into the tire, if compressor does not have a water separator ),,,,rusts out the spring in the pencil. Use digital gauges ( I use 2 and double check )....On a separate note, don't get new tires mounted on humid days. Do it when humidity is 50% or lower. Or, you're tire may be 1/4 full of water instead of air, depending if compressor has a separator attached to it. I only get tires mounted in the spring or fall when humidity is low. Water in a tire will lead to corrosion around the bead area causing leaks.