Answer... when it's an estimate.
Today I read my electricity and gas meters and entered the readings into my online account. I have used only 0.5 cubic metres of gas since last month (current reading on 20 June 24276.5 cubic metres; reading on 20th May 24276.0cubic metres) but as there's no facility to submit digits to the right of the decimal point, the reading I entered was 24276 on both occasions
After entering the reading today I was rewarded with an on-screen message saying that my reading was the same as last months (which it was, for the above reason). There also was an on-screen message saying that the last reading, on 28th May was... and it gave a number I can't recall - but it was GREATER than 24276. And neither I nor anyone else made a reading on 28th May!
When I phoned to draw their attention to this, I was advised that the 28th May number was an ESTIMATE!. I've no real problem with energy companies estimating my usage based on previous usage so long as their method is mathematically sound. BUT THEY CANNOT CALL AN ESTIMATE A READING - OR VICE VERSA. Their phone representative said that their use of the word "reading" kept the web page "cleaner". Well that's a new one! The page can be as clean as they like, but no amount of cleanliness can correct a factual error.