Relativistic red shift with 1 10 16 uncertainty at the NIST, Boulder

The relativistic red shift for the new caesium fountain at the National Institute of Standards and Technology (NIST) at Boulder, USA, has been estimated using two independent methods. Method 1 uses the EGM96 geopotential model to estimate the geopotential number, C , and subsequently the frequency offset, − C / c 2 ( c being the speed of light), obtaining the value 1797.8 × 10 −16 with an estimated standard uncertainty of 1.1 × 10 −16 . Method 2 uses the geopotential number from the National Geodetic Survey data sheet for the NIST marker and gives a frequency offset of 1798.9 × 10 −16 , with an estimated standard uncertainty of 0.2 × 10 −16 .