The International Time Bureau (BIH) began a time scale, Tm or AM, in July 1955, using both local caesium clocks and comparisons to distant clocks using the phase of VLF radio signals. The BIH scale, A.1, and NBS-A were defined by an epoch at the beginning of 1958 The procedures used by the BIH evolved, and the name for the time scale changed: A3 in 1964 and TA(BIH) in 1969.
the international time bureau (bih) began a time scale tm or am in july 1955 using both local caesium clocks and comparisons to distant clocks using the phase of vlf radio signals the bih scale a1 and nbs-a were defined by an epoch at the beginning of 1958 the procedures used by the bih evolved and the name for the time scale changed a3 in 1964 and ta(bih) in 1969