I've also got a pinetime watch, never been a fan of the data collection smartwatch companies do, its great to have something that I know exactly how it works with its open source firmware. It's not exactly perfect but there's been tons of updates from contributions by the community, I've even been able to make some modifications of my own too.
If anyone here in the comments has any questions about it I'd be happy to answer them
Turns out it'd be a dissapointingly small sphere:
US annual defence budget = $800 billion
2% = $16 billion
Obsidian cost per kg = $5
Total kg in budget = 3.2 billion kg
Density of obsidian = 2.6 g/cm3 = 2600 kg/m3
Total volume of sphere = 3.2b/2600 = 1230769 m3
Volume of sphere = 4/3 π r^3
Radius = (3V/4π)^(1/3) = 66.48 m
The sphere would only stand at 133m tall, I propose we instead utilise the entire defence budget for a much more skyscraper like 490m tall orb