The purpose of the rulers is to do some measurements in amplitude and frequency, therefore, these rulers should be calculating, i.e. not only showing each their value by numbers, but also their difference.
Vertical (both in spectrum and sonagram/waterfall). There should be at least three rulers:
- one for the carrier frequency
- two for the bandwidth of the signal
If there is no carrier (as e.g. in SSB), you need only two rulers.
Horizontal (makes just sense in the spectrum). There should be at least three rulers:
- one ruler for the noise level
- one ruler for the carrier
- one ruler for the modulation
With these six rulers you may do a lot of measurements, also according to ITU, e.g.:
- SNR (carrier/signal vs. noise floor)
- bandwidth (-3 dB/-6 dB/-12 dB ...)
- degree of modulation
If these rulers can be coupled, you may obtain something of a "mask". Then you can go (i.e. in the broadcast bands) from channel to channel to measure if the signals comply with specifications.
An additional pair of rulers would provide even the measurement of spurious transmission in a row.
I made up a raw drawing of the suggested rulers, f = frequency, p = amplitude (power); see attachment.
For exact measurements, the level rulers must refer to the resolution bandwidth of spectrum/sonagram. The most professional approach is to do an automatically calculation which gives the level in dBm, refered to dBm/Hz.
73 Nils, DK8OK