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{{anchor|Gillham}}The code is named after Ronald Lionel Gillham, a signals officer at Air Navigational Services, [[Ministry of Transport and Civil Aviation (United Kingdom)|Ministry of Transport and Civil Aviation]], who had been appointed a civil member of the [[Most Excellent Order of the British Empire]] (MBE)<!-- unclear if this was related to his involvement with this code, or for some other achievements --> in the Queen's [[1955 Birthday Honours]].<ref name="LG_1955-06-03"/> He was the UK's representative to the [[International Air Transport Association]] (IATA) committee developing the specification for the second generation of air traffic control system, known in the UK as "Plan Ahead", and is said to have had the idea of using a modified Gray code.<ref group="nb" name="NB_Anecdote"/> The final code variant was developed in late 1961<ref name="Ashley_1961"/> for the ICAO Communications Division meeting (VII COM) held in January/February 1962,<ref name="IEEE_1983"/> and described in a 1962 [[FAA]] report.<ref name="FAA_1962"/><ref name="FAA_1962_T6"/><ref name="FI_1964"/> The exact timeframe and circumstances of the term ''Gillham code'' being coined are unclear, but by 1963<!-- not a specific date, just the earliest source using the term I could find so far. --> the code was already recognized under this name.<ref name="CS_1963"/><ref name="CE_1963"/> By the mid-1960s the code was also known as ''MOA–Gillham code''<ref name="Wheeler_1969"/> or ''ICAO–Gillham code''. ''ARINC 572'' specified the code as well in 1968.<ref name="ARINC_572"/><ref name="ARINC_572-1"/>
Once recommended by the [[ICAO]] for automatic height transmission for air traffic control purposes,<ref name="FI_1964"/><ref name="Wightman_2017"/>
== Altitude encoder ==
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