Patent classification systems

There have been many patent classification systems, and any that helpfully classify aero patents in our period are relevant to include here.

• the CPC category system is the most modern and global, started 2010
• the IPC is the predecessor to the CPC, started 1971, per Wang (2018)
• IPC1-7 - an IPC version or variant
• French patent classifications -- dated in 50-year gropus from about 1858 to 1904 then from 1904 to 1958
• USPC -- US standards used officlally till at least 2013, start date uncertain
• NBER patent classification - a grouping of the USPC system into larger simpler clusters, used in economics research especially
• German patent classifications -- starting 1878 or thereabouts
• Canadian patent classifications -- seems to look a lot like the USPC but the history of it is not known yet ; it was used till circa 1989
• Belgian patent classifications
• British patent classifications

Enclosing categories	Techtype
Subcategories	CPC, IPC, IPC1-7, French patent classifications, USPC, German patent classifications, Canadian patent classifications, NBER patent classification, Belgian patent classifications, British patent classifications
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