In short: a single master air gage is set with one master at nominal and relies on factory-matched tooling and readout for its scale. A dual master gage is set with a low and a high master, so the span itself is calibrated. Single master is faster and cheaper to run; dual master is more flexible and most accurate right at the tolerance limits.
How single master works
The gage is zeroed on one master, usually at the nominal size. Sizes above and below are read using sensitivity built in at the factory: the readout is verified against master orifices, and the tooling jets are finished to a matched sensitivity. Because the accuracy lives in that matched pair, the readout only works correctly with tooling of the same amplification. This is how the Dimensionair-style systems work, and why the Air Gage Pro M5-L and M5-H are matched to specific tool codes.
How dual master works
The gage is set with two masters at or near the low and high limits. The operator adjusts zero and magnification until the readout spans exactly the difference between them. That single adjustment absorbs the small errors of every part of the circuit: restrictors, jets, amplifiers and even pressure losses in the hoses. So the individual components don't need tight matching, and one readout can work with virtually any brand of two-master tooling.
Where the accuracy lands
With a single master, any scale-factor error grows with distance from the master. With a 5% scale-factor allowance, a reading 0.0002″ from the master carries about 0.00001″ of error; at 0.0010″ away it is about 0.00005″. So a single master gage is most accurate at nominal and least certain at the tolerance limits. A dual master gage is the reverse: it is calibrated directly at the limits, where accept/reject decisions are made.
Side by side
| Single master | Dual master | |
|---|---|---|
| Masters per size | One | Two (low and high) |
| Setup | Fast; one master to handle | Slower; span adjusted each time |
| Best accuracy | Near nominal | At the tolerance limits |
| Tooling and readout | Must be pneumatically matched | Works with any two-master tooling |
| Master cost | Lower, especially in large sizes | Higher; two masters to certify |
| Good fit for | High-volume production near nominal | Wide spans, go/no-go, mixed tooling |
Which should you choose?
Choose single master when setup speed matters, readings stay close to nominal, and you want fewer masters to buy and recertify. Choose dual master when you need the limits themselves verified, the measuring span is wider, or you want one readout to run tooling from several sources. Both, properly applied, deliver the accuracy most applications need.
Already have one or the other? The Air Gage Pro M5 Dual runs two-master tooling, and the M5-L and M5-H run single master tooling.
Download the full comparison (PDF)