PURPOSE: To improve measurement accuracy by sampling signals that are subjected to noiseat the most effective time intervals, namely during the continuation of the steady level of a measurement target.

CONSTITUTION: Each black dots the drawing indicates the samples of signals that are subjected to noise and the signal is applied to the display device of a spectrum analyzer. The signal is in trapezoid and a horizontal steady level is displayed at the center of a screen. Sample values range, for example, 0 to 255. With the measurement of the values of a steady level, first, the scale 0-255 is divided into sections each consisting of two units, and the number of samples with values included in each section is counted. Then, a section (217 or 218) with the largest number of samples is examined. The steady level is regarded as being at the section of the values 217 and 218. Then, a value (dB) that is related to the reference value is calculated from the setting parameters of an analyzer.