Even when perfectly calibrated in the mid-range, in our experience all analog SCUBA SPGs (including the ones we sell) have poor accuracy at the low end of the scale; possibly indicating significantly more (or less) breathing gas than what is really in the tank.

SPG manufacturers all seem to reference the EN250 SCUBA equipment standards from the European Union for their accuracy specification of these devices; in terms of a percentage, from about ±5% in the middle range to ±10% in the low range of the scale. In contrast, digital pressure gauges built in to air integrated (AI) dive computers are typically accurate to ±1% across their entire range.

Just to be clear, this is not a reflection on the quality of the gauge but rather a limitation of the mechanical Bourdon tube technology when placed into the relatively small case sizes required for SCUBA applications. For details see our TekTip Inside Submersible Pressure Gauges.