I didn't the attenuation figures were taken some years ago from what people were posting on forums and then averaged out, now removed seen as people 'feel' they are wrong

In reply to a post by BatBoy:

How do you get from the values reported by pbparams to a single figure?

The VDSL2 specification has a definition of "electrical length" that is:

electrical length: An estimate of the loop attenuation, assuming that all sections of a loop obey a sqroot(f) attenuation characteristic. Specifically, the electrical length is the attenuation, in dB at 1 MHz, of an equivalent hypothetical loop with a perfect sqroot(f) attenuation characteristic.

NOTE � The attenuation caused by bridged taps does not follow a sqroot(f) characteristic, and thus the effects of bridged taps may not be accurately represented in the estimate.

Later on, the specification requires a modem to estimate its electrical length, and allows it to use one of two methods.

In essence, though, the modem needs to calculate, for any frequency f, the value loss(f)/sqroot(f). The electrical length is then given from the minimum value of these, for all frequencies from 1MHz upwards, of all workable frequencies.

That definition works for across the whole spectrum. Presumably the pbparams output just tells you the "min" value for subsets of the spectrum.