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[konrado5]

I've found in ITU-T G.922.3 specification some information about Hlog measurement accurracy (page 113).

The accuracy requirements for the downstream HLOGps (HLOGps_ds and HLOGps_us) shall
apply only for those frequencies where the loop impedance (Z loop ) falls within the following ranges:
• impedance magnitude is between 100 Ω and 120 Ω;
• impedance imaginary component is between –20 Ω and 0 Ω.
The loop impedance (Z loop ) is defined as the impedance seen by the transceiver under test, looking
into the loop, including the transmitting transceiver connected to the loop at the far end

Does somebody know what is about?

[Weaver]

I wonder which operators / lines they might be talking about?

[konrado5]

I've found also appendix VIII of g 922.3 specification.

This appendix provides a discussion regarding the effects on measured accuracy of Hlog when there
is a mismatch between a nominal loop termination impedance of 100 Ω and the actual termination
impedance (Z ATU ) provided by the ATU. This appendix is meant to provide additional technical
details regarding clause 8.12.5.1.1 on accuracy requirements for the HLOGps test parameter.

http://www.itu.int/rec/T-REC-G.992.3-200904-I/en

[konrado5]

Interesting patent.
https://patents.google.com/patent/US20080288190

[konrado5]

I wonder which operators / lines they might be talking about?

They are not talking about specific lines/operators. They are talking about ADSL technology. I wonder if it is often that circuit have impedance causing hlog measurement errors.