[2] NIST have attributed the clock's accuracy to the fact that it is insensitive to background magnetic and electric fields, and unaffected by temperature.
[3] In March 2008, physicists at NIST described an experimental quantum logic clock based on individual ions of beryllium and aluminum.
[4] In February 2010, NIST physicists described a second, enhanced version of the quantum logic clock based on individual ions of magnesium and aluminium.
[5] [6] In terms of standard deviation, the quantum logic clock deviates one second every 3.68 billion (3.68 × 109) years, while the then current international standard NIST-F1 Caesium fountain atomic clock uncertainty was about 3.1 × 10−16 expected to neither gain nor lose a second in more than 100 million (100 × 106) years.
[15] In 2015 JILA evaluated the absolute frequency uncertainty of their latest strontium-87 429 THz (429228004229873.0 Hz[16]) optical lattice clock at 2.1 × 10−18, which corresponds to a measurable gravitational time dilation for an elevation change of 2 cm (0.79 in) on planet Earth that according to JILA/NIST Fellow Jun Ye is "getting really close to being useful for relativistic geodesy".