*fixes glasses even though I don't wear them and speaks in nasally voice* Actually, 1" = 2.5 cm is imprecise, not inaccurate. ...sorry, I had to take a break from all this intent stuff :P.
Regarding Interplanetary measurements: Officially it was all supposed to be in CM, however many people who got paired up to play agreed to use inches as that's what they usually used.
Actually... :tearsofjoy: As it's wrong by exactly the same amount each time, it's precision is 100%, but because it's always wrong it's always inaccurate...
Indeed, if you are talking about multiple measurements, you are correct. On the other hand, a single measurement's precision is denoted by it's number of digits and if you can only measure to the cm (guessing at the mm value), then you are more likely to measure 2.5 cm than 2.6 cm when measuring an inch... hence, the accuracy.
Since Sweden is very much into the whole "original English" version of rules, the only game I've ever seen anyone play in cm is a GW game. Now, a Swedish duodecimal inch is 24.74mm*, unless it's the newer decimal inch (where a foot was 10 inches) where it was 29.69mm*. Luckily because of el cheapo importing it's guaranteed to only be imperial inches on our measurement implements and most likely double-sided with inches on one side and metric on the other. Also, the fact that Sweden dropped inches in 1889 does play into it somewhat. * Unlike Imperial Inches, old and new Swedish inches were never changed to be easily convertible to metric so those numbers are rounded.
For some reason cm seems somehow wrong to me ;/ (in tabletop, IRL they rock over inches ;P) <insert obvious joke here>