A hobbyist who blogs as Chip Overclock wasn't satisfied with his GPS-disciplined desk clock. The Raspberry Pi inside it kept time within microseconds of UTC, but only when GPS satellites were available. Lose the signal during bad weather or an antenna glitch, and the Pi's standard quartz oscillator would start drifting. He wanted something that wouldn't. He needed an atomic clock. He named his projects after the 18th-century British carpenter John Harrison, whose H-1 through H-5 chronometers chased the Board of Longitude prize (the story Dava Sobel told in Longitude ). His own clocks became O-1, "hourglass," and O-2, "astrolabe." O-2 runs on a cesium-133 oscillator, the active element of any atomic clock, built into a surface-mount chip. That part exists because DARPA funded its development through two research solicitations in 2001 and 2008, seeking a portable atomic frequency standard for military applications such as navigation and munitions. Symmetricom delivered the SA.45s.…