Get crowding information

When getting crowding information of a StopPoint (for example, using the crowding endpoint for getting information about South Kensington Underground, https://api.tfl.gov.uk/crowding/940GZZLUSKS), what does the value percentageOfBaseLine represent, is it an abstract unit? I can’t seem to find this in the documentation.

Also, South Kensington Underground is supposed to be closed until next year, so is this endpoint reliable?

South Kensington is only closed to the Piccadilly line while the escalators down to those platforms are replaced. The station itself is still open, and Circle and District line trains still stop at platforms 1 and 2.

Though I believe that even if the station was closed, crowding information would still be available despite the lack of passengers, as the crowding API currently uses historical WiFi connection data. TfL do however plan on releasing near real-time data in the summer of this year, so at that point the crowding info would likely reflect any closures.
(source: New WiFi data API)

Unfortunately I am not aware of exact what the percentageOfBaseLine value represents and have been struggling to figure it out myself. Perhaps @jwithers could be of some help here, as they announced the availability of the crowding API.

Thanks for your answer, I have also suffered trying to find out, I thought it would be a percentage whose total sum would give 1 in a day or in a week, but seems like no!