Stability

Stability in metrology is the consistency of measurement results over time — a stable measurement system produces the same results today, next week, and next month when measuring the same artifact, indicating that the gage is not drifting or degrading.

Stability Assessment

• Method: Measure the same reference standard (master part) periodically — daily, weekly, or each shift.
• Control Chart: Plot measurements on a control chart — detect drift, trends, or sudden shifts.
• Time Frame: Assess stability over the period between calibrations — gage must remain stable between cal cycles.
• Environment: Temperature, humidity, and vibration changes can affect stability — control the environment.

Why It Matters

• Calibration Interval: Stability determines how often the gage must be calibrated — unstable gages need frequent calibration.
• Drift: Slow drift can go undetected without stability monitoring — causing gradually increasing measurement error.
• Semiconductor: Fab metrology tools run 24/7 — daily stability checks using "golden wafers" are standard practice.

Stability is the measurement staying true over time — ensuring the gage produces consistent results throughout its calibration interval.