The optional Dial Gauge gives accurate readings of how much air is in your Spare-Air in 200 psi increments with 1000 psi numerical readout. The most popular add-on feature shows the amount of air in Spare Air Cylinder. You can order your Spare Air with the Dial Gauge already installed or you can simply install one in any Spare Air. Gauge face has green for safe level and red for needs refill level allowing readings at a glance. Durable brass construction.