[mcphage]

> instrumental readings- there's no information in the text that supports this interpretation.

From the story: “A curious feature of the station is its powerful gravitational field, far stronger than would be suggested by its small mass. However, this probably represents a faulty reading by our instruments.”

And then the next paragraph is the estimated size.

> but at a second look makes his character incoherent because he's contradicting what he just wrote.

His character was incoherent from the first look, too.

[throw310822]

Yes, they have instruments and they ignore their readings when they appear to diverge wildly from their assumptions. (Here the mention of gravity is confusing because that's one thing you don't need an instrument to measure and that directly translates to mass- but I interpret the sentence you quoted as meaning: "our instruments read a powerful gravitational field that doesn't match with the mass reasonable for a 500 metres station, so it's probably a faulty reading").

In any case, the following report clarifies:

"To our surprise we find that the station is far larger than we guessed. [...] This fine vapour obscured the substantial bulk of the station and led us to assume that it was no more than a few hundred metres in diameter."

So the reporter refers to his previous estimate as a guess, not a measurement, and specifies that the assumption was based on what they could see. The following estimates are similarly guesses based on their current understanding and explorations, not the output of some specific instrument.