NIST F1 (cesium fountain time standard)

[Tom shows a slide of NIST F1.] Here's NIST F1. This is the time standard for the world. You need kind of a room about this size to hold it. And here is what they've been able to do since the early '50s — NBS-1 (it used to be National Bureau of Standards) through NIST F1. There was a NIST 7. This is the improvements: one part in 10 to the 15th. This is the frequency uncertainty. So it's 10 to the -15. One part in 10 to the 15th. Anybody know what that's equivalent to in terms of seconds? There's about 10 to the 8th seconds in a year. So this is one second in thirty million years — my notes say thirty billion. Anyway. Someday they'll find another one even better. But we can measure time better than anything else because we're looking at the frequency of a cesium atom vibrating.