Optima Calibration Caps Dive Rite # DRT-27-CAL O2ptima divers who want a fast method for sensor calibration without having to fill the loop can now use our Calibration Caps. They help to conserve gas with small cylinders. We came up with a calibration cap set that consists of an inlet cap with a BC hose connection to plug your manual oxygen hose into and an exhaust cap fitted with a mushroom valve so you can evacuate the canister and fill it with oxygen for calibration. Since it is a mushroom valve you can’t overpressurize the canister while calibrating. It’s simple to use and carry with you.