Rujukan Jam_bandul

  1. ↑ Milham, Willis I. (1945). Time and Timekeepers. New York: MacMillan. ISBN 0-7808-0008-7. , p.330, 334
  2. ↑ Marrison, Warren (1948). "The Evolution of the Quartz Crystal Clock". Bell System Technical Journal. 27: 510–588. 
  3. ↑ Milham 1945, p.74, 197–212