Measurement of quadratic mean deviations by means of a cathode-ray tube

Conclusions

The above method can be applied not only to processes with a normal distribution law. If the signal amplitudes are distributed according to an equal probability law, which is apparent from the glowing of the screen, the quadratic mean deviation in this instance can be determined from the width Δ of the uniformly glowing strip on the screen by expressing it in volts:

$$\sigma=\frac{\Delta}{2\sqrt{3}^.}$$

In the case when the brightness of the oscillograph line is uniformly reduced from the center to the peripheries (in both directions) which corresponds to a linear distribution law, the quadratic mean deviation is calculated from the formula:

$$\sigma=\frac{\Delta}{2\sqrt{2}^.}$$

It is possible to obtain by means of the basic propositions of the theory of probability similar relationships for some of the other probability distribution laws of signal amplitudes.