Inch has been changing over times and places....I tired to find direct link, but could not.
There is an interesting table on this document on page 7 -8
https://emtoolbox.nist.gov/Publications/NISTMonograph180.pdfThe English system of units was based on a yard bar, another artifact standard [6].
These artifact standards were used for over 150 years. The problem with an artifact standard for
length is that nearly all materials are slightly unstable and change length with time. For
example, by repeated measurements it was found that the British yard standard was slightly
unstable. The consequence of this instability was that the British inch ( 1/36 yard) shrank [7], as
shown in table 1.1.
Table 1.1
1895 - 25.399978 mm
1922 - 25.399956 mm
1932 - 25.399950 mm
1947 - 25.399931 mm
1.2 The Inch
In 1866, the United Stated Surveyor General decided to base all geodetic measurements on an
inch defined from the international meter. This inch was defined such that there were exactly
39.37 inches in the meter. England continued to use the yard bar to define the inch. These
different inches continued to coexist for nearly 100 years until quality control problems during
World War II showed that the various inches in use were too different for completely
interchangeable parts from the English speaking nations. Meetings were held in the 1950's and
in 1959 the directors of the national metrology laboratories of the United States, Canada,
England, Australia and South Africa agreed to define the inch as 25.4 millimeters, exactly [9].
This definition was a compromise; the English inch being somewhat longer, and the U.S. inch
smaller. The old U.S. inch is still in use for commercial surveying of land in the form of the
"surveyor's foot," which is 12 old U.S. inches.