Which statement best describes offset and gain error in sensor measurements?

• A. Offset is a random drift; gain error is caused by noise.
• B. Offset is a proportional scaling error; gain error is a constant offset.
• C. Offset is a constant added or subtracted output; gain error is a proportional scaling error.
• D. Offset and gain error have no effect on the transfer function.

Answer: (C)

Offset and gain error describe how a real sensor’s output deviates from the ideal transfer function. In an ideal sensor, the output y relates to the input x by a simple scaling: y = G_nominal × x. In practice, the relationship is y = G_actual × x + b, where b is the offset and G_actual is the actual gain. The offset is a constant added (or subtracted) to the output regardless of input, so even with zero input you get a fixed reading. Gain error is a proportional scaling error because the slope, G_actual, differs from the intended G_nominal, altering how the output grows with input. This makes the described statement the best fit: offset is a constant added or subtracted output, and gain error is a proportional scaling error. The other descriptions mix up which term is constant versus proportional and ignore how both terms modify the transfer behavior.