Rolling action of elastomeric Series 1500 measures differences in pressure between 2 points in system. Diaphragm is combined with piston-magnet pointer assembly to completely seal piston area, which allows measurement of high differential pressures up to 300 psid. Pressure instrument incorporates anodized aluminum, Type 316 stainless steel, naval brass or PVC body, and wetted parts. Switch and gauge-switch models measure over 18 pressure ranges from 0-5 to 0-300 psid.