Question 3-75L4

Analog wattmeters, like many analog measuring devices, typically specify their accuracy as a percentage *of full scale*. This means the absolute error value (e.g., +/- 5 watts) is determined by the maximum reading of the meter and remains constant across the entire scale. Therefore, the most accurate *relative* reading will occur at or near full scale. For instance, a 100-watt meter with 5% full-scale accuracy has an absolute error of +/- 5 watts. When reading 100 watts, the error is 5% (5/100). However, if you read 20 watts, the same +/- 5-watt absolute error now represents a much larger relative error of 25% (5/20). * **A is correct** because the absolute accuracy number derived from the full-scale specification is indeed applied across the entire range. This makes readings closer to full scale more *proportionally* accurate. * **B is incorrect** because while the *absolute* error value might be constant, the *relative* accuracy (percentage error) is not constant; it degrades significantly at lower readings. * **C is incorrect** because the accuracy specification isn't limited to just the top 5%; the full-scale error value applies to all readings. * **D is incorrect** because meter accuracy specifications are a fundamental part of their design and are always determinable.