Nonlinearity in an instrument means:

• A. Random noise
• B. Deviation from a straight-line response across the range
• C. Temperature effects
• D. Hysteresis

Answer: (B)

Nonlinearity means the output does not scale proportionally with the input across the operating range. A linear instrument shows a straight-line relationship between input and output, so doubling the input would double the output (aside from a constant offset). When nonlinearity is present, the transfer curve bends, so the gain changes with input level and the same input step can produce different output changes depending on where you are on the range. This causes distortion or saturation in the response.

Some related phenomena aren’t nonlinearity in this sense: random noise adds unpredictable fluctuations, temperature effects cause drift over time or with temperature, and hysteresis is a lag that depends on the history of input. But nonlinearity specifically describes that curved, non-straight transfer characteristic.