A matchbook-sized atomic clock 100 times smaller than its commercial predecessors has been created by researchers. The portable Chip Scale Atomic Clock — only about 1.5 inches on a side and less than a half-inch in depth — also requires 100 times less power than its predecessors. Instead of 10 watts, it uses only 100 milliwatts. “It’s the difference between lugging around a device powered by a car battery and one powered by two AA batteries,” said the lead investigator.