klein bottle mugs that also manage to double as barometers. it’s taken me far too long to get my head round how they’ve managed to make usable mugs out of something that has no inside.

• displacement 825 ml (28 fluid ounces) about half a [us] pint inside, half a pint outside.
• actual volume 0.0 ml (0 fluid ounces) zero inside, zero outside.

[found via uncertain principles]