Inter-range instrumentation group timecodes, commonly known as IRIG timecode, are standard formats for transferring timing information. Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG output. The standards were created by the Tele Communications Working Group of the U.S. military's Inter-Range Instrumentation Group (IRIG), the standards body of the Range Commanders Council. Work on these standards started in October 1956, and the original standards were accepted in 1960. The original formats were described in IRIG Document 104-60, later revised and reissued in August 1970 as IRIG Document 104-70, upgraded later that year as the IRIG Document to the status of a Standard, IRIG Standard 200-70. The latest version of the Standard is IRIG Standard 200-16 from August 2016. Timecodes The different timecodes defined in the Standard have alphabetic designations. A, B, D, E, G, and H are the standards currently defined by IRIG Standard 200-04. C was in the original specification, but was replaced by H. The main difference between codes is their rate, which varies between one pulse per minute and 10,000 pulses per second. The bits are modulated on a carrier. A three-digit suffix specifies the type and frequency of the carrier, and which optional information is included: Modulation type DC level shift (DCLS) (pulse width coded without carrier) Sine wave carrier (amplitude modulated) Manchester modulated Carrier frequency No carrier (DCLS) 100 Hz (10 ms resolution) 1 kHz (1 ms resolution) 10 kHz (100 µs resolution) 100 kHz (10 µs resolution) 1 MHz (1 µs resolution) Coded expressions Binary-coded decimal (BCD) day of year, hours, minutes, and (for some formats) seconds and fractions are always included. Optional components are: Year number (00–99; century is not coded) User-defined "control functions (CF)" occupying bits not defined by IRIG "Straight binary seconds (SBS)", a 17-bit binary counter that counts from 0 to 86399. The types are:BCD, CF, SBSBCD, CFBCDBCD, SBSBCD, BCD_Year, CF, SBSBCD, BCD_Year, CFBCD, BCD_YearBCD, BCD_Year, SBS The recognized signal identification numbers for each format according to the standard 200-04 consist of: Thus the complete signal identification number consists of one letter and three digits. For example, the signal designated as B122 is deciphered as follows: Format B, Sine wave (amplitude modulated), 1 kHz carrier, and Coded expressions BCDTOY. The most commonly used of the standards is IRIG B, then IRIG A, then probably IRIG G. Timecode formats directly derived from IRIG H