January 14, 2016 at 03:14AM

Today I Learned: 1) Continuing with my SpaceX-related posts, I watched part of a video tour of SpaceX headquarters, circa 2011. There were a couple of interesting tidbits -- for one thing, they have a shop that checks the precision of their machined parts down to about a thousandth of an inch to make sure they're perfect. Little details like that matter when building a rocket. The precision-checking room is kept temperature controlled at 68F -- if it wasn't, the metal would expand or contract, making precision measurement impossible. Part of me wonders why the rocket would ever work if tolerances have to be that good... but maybe it's ok if everything expands an contracts together? Or perhaps the really important parts are kept temperature-controlled during launch? Another interesting tidbit -- SpaceX's conference rooms are glass-walled, but those walls are rigged with motion sensors to turn foggy when someone enters the room. Musk seemed quite pleased about those walls. 2) ...fingering for a couple of minor scales I'd never learned before (for piano). 3) In longitudinal studies (not the best, I know), there is no evidence that smoking marijuana is associated with higher mortality or any obvious disease. This is a little surprising, since smoking tobacco certainly is. Are cigarettes just ridiculously efficiently packed with toxins? Would a fresh tobacco leaf rolled up in paper be safe to smoke?