I'd have to presume that it's the radius of the [buried] artifact, and not not the accretion crust, since A) the latter is subject to change over time (as it collects more material) and more importantly B) is unlikely to be so perfectly spherical that Tagii is unable to detect a difference in ratio to more significant digits then she has the ability to measure. Of course that implies also that the artifact itself has that level of precision in it's surface, but as an engineered rather then randomly accreted object that's not beyond the realm of belief.
speaking of which, is it just me, or is there something grammaticly wrong with Tagi's sentence, when she says
"I Don't have the instrumentation to get past the number of significant digits where it is not"
I keep thinking that what she technically said was that to all her instruments, the multiplication factor radius was NOT quite perfect, but she believed it would become perfect if she had better instruments.
Although I suppose that could actually make sense..... if she was trying to measure a multiplication of 2063 down to the millimeter, and her instruments just weren't that good, she would wind up measuring a distance to the nearest meter, which was almost, but not quite, exactly 2063 times the radius, while she was confident that with better instruments, it would work out to be exactly 2063....