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:: Those standards are predominately based on the two leading Numerically Controlled mills during the APT work: the Giddings & Lewis mill (trademarked as the Numericord) which used a combination of General Electric and Concord Controls controllers. The second system was the Kearney & Trecker mill, which used a Bendix controller. Both machines had detailed papers published at the Eastern Joint Computer Conference in December 1957 (proceedings available online). The Bendix solution used "R-codes" to describe operational modes (essentially G-codes) and another set to describe auxiliary on/off functions (essentially M-codes). The Giddings & Lewis system used "X-codes" which also described operational modes and auxiliary on/off functions. These are the X-codes described in the APT flowcharts. The assertion that these were the two leading NC mills in the mid-50s can be found in <i>Forces of Production</i> by David F. Noble. The same book contains significant content as to why Bendix became the preferred solution during the standardization process.
:: The X-codes are better documented in US patent 2963137 "Controls for a typewriter and associated apparatus" (the patent title is somewhat misleading - this is a numerical control patent). The patent assignee is Giddings & Lewis, but the four inventors (McDonough, Susskind, Grossimon, and Lee) were all MIT staff attached to the Servo Lab. Giddings & Lewis poached the entire numerical control staff (with the exception of Susskind) to form Concord Controls at the beginning of 1956. Note that the same team worked on the original MIT NC Mill, which was finalized in 1952. Bendix licensed the two patents that were generated from the 1952 mill.
:: The Bendix R-codes were encoded on punch tape in their own special block, so there was never an appearance of an alphanumeric code, such as "R00". The Giddings & Lewis X-Code, however, appeared exactly as G-Code would later be used. There is no relationship between the operational code numbers between X-Code and the later G-code. It's unknown if the same can be said for the auxiliary functions, as they are deliberately not documented in the 1957 paper, nor the 1956 patent - other than the Program End function which was encoded as "X00", the same as the later "M00". (see the part programming sheet, Figure 5, of the G&L patent).
::[[User:Alvonruff|Alvonruff]] ([[User talk:Alvonruff|talk]]) 15:17, 16 September 2021 (UTC)
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