Resolution tells you how finely an instrument can display a change. Accuracy tells you how close the indicated value is expected to be to the actual value within the instrument's stated specification. A good gauge specification should make that distinction clear.
An instrument can show many decimal places while still having a relatively broad accuracy tolerance. Resolution and accuracy should always be evaluated separately.
What is resolution?
Resolution is the smallest increment the instrument can display or meaningfully distinguish. On a digital gauge, this is usually easy to see because the display changes in defined steps.
For example, a gauge with 0.1 inHgV display resolution can show readings such as 29.6, 29.5 and 29.4 inHgV. That makes a one-tenth change visible without estimating between marks on a dial.
What is accuracy?
Accuracy describes how close the indicated reading is expected to be to the actual pressure or vacuum value under the conditions defined by the manufacturer.
Accuracy is typically expressed as a tolerance, percentage, fraction of full scale or another defined specification. The exact wording matters because different manufacturers may specify accuracy in different ways.
Useful for seeing movement, comparing readings and recording small changes during process verification.
Important when the process requires confidence that the indicated value falls within a defined measurement tolerance.
Why the two are often confused
Digital displays can create an impression of precision because the reading is shown numerically. But a display that shows tenths or hundredths does not by itself establish how accurate the underlying measurement is.
Likewise, an accurate instrument may have a relatively coarse display. It may be capable of measuring within a tight tolerance while only presenting the result in larger increments.
A simple example
Those steps tell you something about the gauge's display resolution. They do not, by themselves, tell you the instrument's accuracy. The accuracy must come from the separate stated specification.
Why both matter in composite manufacturing
Resin infusion and vacuum-bagged processes often involve two different measurement needs.
- Operators may need to see small changes during leak checks, stabilization or timed vacuum drop testing.
- Quality or engineering requirements may also define how accurate the measurement instrument must be.
Resolution helps make small movement visible. Accuracy helps establish confidence in the numerical value being reported.
How the DVS-G specifications are stated
The DVS-G has a display resolution of 0.1 inHgV and a stated accuracy of ±0.075 inHg. Those are separate specifications because they describe different aspects of instrument performance.
The 0.1 inHgV display increment makes subtle changes easier to observe, while the accuracy specification describes the expected measurement tolerance.
Evaluating a gauge specification
When reviewing a gauge for a manufacturing process, look beyond the number of digits on the display. Consider the complete specification and how it relates to the process requirement.
- What is the display resolution?
- How is accuracy specified?
- Is accuracy based on full scale, reading or another reference?
- What environmental or operating conditions apply?
- Does the process require calibration or documented verification?
- Is the instrument range appropriate for the measurement?
Aerospace, defense, space and other quality-controlled programs may define minimum instrument accuracy, calibration status, measurement range or other requirements. Those specifications should determine whether a gauge is suitable for a particular process.
DVS-G DIGITAL VACUUM GAUGE
High-resolution visibility with a clearly stated accuracy specification.
The DVS-G displays vacuum in 0.1 inHgV increments with stated accuracy of ±0.075 inHg for vacuum bagging, resin infusion and process verification.
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