NEW Design Tire Pressure Gauge - Great looking new graphics, now reads in 1/2 lb. increments and includes both angle and ball chucks. 2 1/2" Deluxe Gauge with protective bumper. 1/2 lb. increments with 2% accuracy. Air pressure release button. 17" hose with swivel angle chuck installed with alternate ball chuck included. HOLDS PRESSURE READING UNTIL RELEASED. Glow-in-the-Dark dial face. Specially designed vent valve to equalize pressure and maintain gauge accuracy.Liquid Filled Tire Pressure Gauges ALL liquid filled gauges are purposely filled to just 80%. The remaining 20% air pocket helps allow for thermal expansion and contraction as ambient temperature changes, thereby maintaining accuracy. If the gauge were filled to 100% even the slightest temperature change would significantly affect gauge readings as the expanding fluid would have no place to go. To give you even further accuracy over a wide operating range these Longacre gauges have a Special Vent Valve on the top of the gauge. A quick turn of the knob allows you to totally equalize internal and external pressures, guaranteeing the best accuracy possible.Liquid filled gauges have many advantages. But they can change readings by as much as 2-3 psi if the temperature changes... All pressure gauges - liquid filled and regular - need to be vented to the outside to read accurately. If not vented, as the surrounding temperature changes, they will build up pressure inside and affect the accuracy - by as much as 2-3 psi! But if a liquid filled gauge is vented it will leak on your hands and in your tool box. Some manufacturers arent aware of this and dont vent the gauge. You then have to deal with the variation in accuracy. Now from Longacre comes the simple answer to this problem. We have installed a specially designed pressure equalizer valve on the top of the gauge. Before you use the gauge just loosen the knob on top of the gauge 1/4 turn, then hand retighten