BT Availability Checker - results 'range' updated.

I moved to an FTTC connection last month.

My original speed estimates according to BT's official Availability Checker were:
FTTC Range A (Clean) High 44.6 Low 33.3
FTTC Range B (Impacted) High 37.8 Low 21.5

Initially I had speeds around 30 (29.14 IP Profile) but these quickly reduced as DLM adjusted things. I now seem stable around 23Mb.

I've been monitoring the 'checker' to see if speeds change and they have today.
FTTC Range A (Clean) High 29.3 Low 20.6
FTTC Range B (Impacted) High 23.4 Low 11.5

Even though these speeds were lower than I expected on an approx 700m line the new estimates do seem more accurate.

BT's ADSL 'estimates' were always well out. Showed 2 or 3 for me when I connected at 6.

Does anyone know how these FTTC estimates are calculated?
Have they been 'adjusted' looking at my actual stats? - this gives a more rosy picture but as with ADSL it might not be an accurate estimate of what you can achieve.

I don't have many neighbours so I can't check many numbers, but the one's I have also seem to have been reduced.

Calculated from paper records rather than someone going around testing all 29 million lines initially.

Then there is feedback from live lines into the system.

As for the exact calculation, no am not privy to it.

I don't think mine have changed again, maybe the low end of the "impacted" range has gone down a bit. I'm currently right on the low end of the "clean" range.

My page has always stated '1 to 3.5'' Mbps on an ADSL Max service and I synced at the full 8128kb/s when connected, with a 6.9Mb/s throughput. My exchange was never upgraded to CN21 so can't comment on published ADSL2+ rates. And I'm not able to use a fibre service yet so can't comment on that until I am.

With the experience I've had/ seen, I'd always take an estimate as just that for my line.

Paul