If you thought Marc Newson's Hourglass design for Ikepod was stunning, wait 'til you see the video of how they manufacture it. This may be my favorite making-of video of all. At the Glaskeller factory in Switzerland, workers manipulate borosilicate glass to Newson's precise specifications using a combination of old and new techniques; as an example of the latter, the sand has been replaced by nanoballs.
I'm curious to know how the heck they calibrate the ten- and sixty-minute durations, but I'll have to wonder a while longer as the video is blissfully free of words or verbal explanations.

Comments
They calibrate the hourglass by adding or subtracting "sand" so that the duration is to spec. The video briefly shows this procedure towards the end.
What an exquisitely clean factory. Thanks, great video.
My guess is they calibrate by adding the right amount of sand.
Not by calibrating the glass. Nice video.
to calibrate the time, of course the sizing of the glasses is different. but i bet they just add sand until they have a perfect 10 or 60 minute hourglass then they seal it up.
they might just add a standard amount a little short of the amount needed and then add more until it is perfect. knowing the flow-rate of the sand would help too.