Which of the following is a source of measurement error that tends to change slowly over time?

• A. Drift (slow change)
• B. Hysteresis
• C. Noise
• D. Resolution limits

Answer: (A)

Drifts describe a gradual, time-dependent change in a sensor’s output that isn’t caused by a changing input. Over days, weeks, or months, components age, conditions vary, and calibration shifts, so the measurement drifts away from the true value. This creates a persistent, slowly evolving error unless you recalibrate or apply compensation.

In contrast, hysteresis is about the output depending on the input history—when you ramp a quantity up and then down, the path taken matters, often producing a loop rather than a slow time drift. Noise is random, rapid fluctuation around the true value, not a steady trend over time. Resolution limits are about the smallest step the instrument can display, a fixed discretization that doesn’t inherently change with time.

So the source of measurement error that tends to change slowly over time is drift. Regular calibration and temperature/aging compensation help keep readings accurate.