180
xkcd #3248: 182.8 Meters
(imgs.xkcd.com)
Title text:
They rounded down to 182.8 instead of rounding up to 182.9 because 182.9 might make the statement incorrect.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3248/
Seems silly to me, if it's a bay, there's silt flowing into it, time itself could pile 10cm of detritus into the deepest parts and make it more shallow.
That's the whole point. 100 phatoms is really imprecise. But on translation, they didn't bother keeping the significant digit count equal, and since 182.8 m= 100 f , they just left it like that. I mean, it's the only reason he could guess there was a unit change...
Or currents might deepen a hole too. Putting silt in one place can cause other places to change too.
And if it were more shallow, shipping would have a big impact too.