which is their estimate of TAI. Time codes are usually published in the form of UTC, which differs from TAI by a well-known integer number of seconds. These time scales are denoted in the form UTC(NPL) in the UTC form, where NPL here identifies the National Physical Laboratory, UK. The TAI form may be denoted TAI(NPL). The latter is not to be confused with TA(NPL), which denotes an independent atomic time scale, not synchronised to TAI or to anything else.

The clocks at different