I dont know …
But i think there is a convention that a certain signal level into a receiver should show a certain VU meter level.
And that level display would be calibrated in computer software … I think that the available software are not matured enough to have that – maybe SdrRadio, but i have always felt that a signal level is some what irrelevant. if it can be heard , good. If not, then improve the signal to noise ratio or gain of the antenna.