Given the question about leap seconds and WWVB, I ran across some old NIST documents that shed light on the evolution of broadcast time services.
Dated 1965, NBS Low-Frequency Station WWVB to Broadcast International Unit of Time http://tf.boulder.nist.gov/general/pdf/1721.pdf This (and a number of other documents of the era) mention the transition from a UT-based time/frequency broadcast to the modern atomic time/frequency standard to respond to the needs of their "customers". Of course this resulted in gradual time drift wrt UT and so the solution at the time was to shift time by 200 ms about every 3 months (which is 12000 60 kHz cycles) -- what could be called a leap fifth second. Dated 1966, WWVB Adds Time Code to Broadcast http://tf.boulder.nist.gov/general/pdf/1731.pdf Here we see when the time code was first added to WWVB. Note back in those days the UT2 correction was broadcast to millisecond resolution and the 3 digit BCD field was updated daily. Later those 12 bits were reallocated to today's format where 2 of those 3 BCD digits are used for the year and the UT1 correction gets just 1 BCD digit and a resolution of 100 ms. Dated 1972, NBS Frequency and Time Broadcast Services; Radio Stations WWV, WWVH, WWVB, WWVL http://tf.boulder.nist.gov/general/pdf/1545.pdf This larger document has more history and time code details for all NBS stations. Note the first mention of leap seconds on page 9 of the PDF, as international time scales switched from the old rate step model (multiples of 50 parts in 10^10) to the new time step model (leap seconds). /tvb _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
