Re: off topic Question of the day..
On Sat 16 Jul 2016 at 19:46:00 (-0500), John Hasler wrote:
> NIST does not agree with you. As for recognizing the metric system and
> making it legal for trade, the USA did that in 1866. What it has not
> done and what the metrification enthusiasts really want it to do is ban
> the use of the customary system.
It's usual to quote the parts of the post that you're referring to.
As you haven't, I'll just put them back in here.
I wrote:
> On Fri 15 Jul 2016 at 22:48:11 (-0500), John Hasler wrote:
> > Dennis writes:
> > > BTW: one inch now equals 2.54 cm *exactly*, in case you haven't been
> > > keeping up! (Used to be approx 2.54 cm.) This is what I mean by
> > > arbitrary. Don't like the conversion ratio? Then just change it!
> >
> > It wasn't a change in conversion ratio. It was change in definition.
> > Originally US length measures were defined by a physical standard
> > derived from the British yard such that the inch worked out to close to
> > 2.54cm. In 1893 the inch was defined as 2.54cm
>
> Close, but no ciger. The 1866-07-28 length of the US yard was
> preserved at 3600÷3937 of the metre. What changed in 1893 was
> the adoption of the International Standard Metre (21 and 27
> were the ones they received) as the prototype.
In 1893, the “Mendenhall Order” was published as Bulletin 26 of the
Coast and Geodetic Survey. It was republished as Appendix 3 of
“Weights and Measures Standards of the United States a brief history”
in Special Publication 447 of the National Bureau of Standards, which
is NIST's predecessor. It says “The practical effect upon our
customary weights and measures is, of course, nothing. The most
careful study of the relation of the yard and the metre has failed
thus far to show that the relation as defined by Congress in the act
of 1866 is in error.”
A footnote at the end of this paragraph says “NOTE---Reference to the
act of 1866 results in the establishment of the following:
Equations.
3600
1 yard = ----metre.
3937 ”
This contradicts the statement “In 1893 the inch was defined as 2.54cm”.
> The change to inch=2.54cm came much later (1959-07-01) and was
> actually expressed as one yard = 0.9144 of the metre. The old foot,
> the US Survey foot, is still used by the National Geodetic Survey
> for the publication of heights. Some states still publish their
> State Plane Coordinates in feet (provided to them by NGS in metres)
> and are at liberty to use either type of foot.
Again from Special Publication 447, §8 (page 20) says “When the
National Bureau of Standards began its work in 1901 the principal
units of weights and measures in the U. S. customary system were
defined as follows:
3600
1 yard = ----metre.
3937
1 pound = [...]
1 gallon = [...]
1 bushel = [...]
These definitions remained unchanged for 58 years, and the last two
are still the official values.
[...
...] and the United States entered into agreement, effective July 1, 1959,
whereby uniformity was established for use in the scientific and
technical fields. The equivalents 1 yard=0.9144meter (whence 1 inch
=25.4 millimeters) and [...] were adopted for each of these national
laboratories.”
Appendix 5 shows the change in length on 1959 to be about 2ppm, and
also states “Any data expressed in feet derived from and published as
a result of geodetic surveys within the United States will continue to
bear the following relationship as defined in 1893:
1200
1 foot=---- meter
3937
The foot unit defined by this equation shall be referred to as the US
Survey Foot and it shall continue to be used [...]”
until they readjust the survey networks, which they did in 1983 with
NAD83, superseding NAD27.
The survival of the US Survey Foot to the present time is evidenced
by http://www.ngs.noaa.gov/faq.shtml which says “NGS does NOT have an
"official" conversion factor. NGS works in meters ONLY. NGS only uses
feet to publish SPCs, and those are converted from meters using the
conversion factor as defined by the individual states who have
requested that we publish SPCs in feet.
The only other instance where NGS publishes linear values in feet is
for elevations, i.e., orthometric heights. All computations are still
done in meters, but for publication purposes we convert meters to
feet. That conversion is done using the U.S. Survey Foot conversion
factor. We publish elevations in meters to the nearest millimeter (3
decimal places) and in feet to hundredths of a foot (2 decimal
places). For elevations above 5,000 feet (1,524 meters), the
conversion factor will change the foot value by one in the second
place.”
If NIST does not agree with its own historical publications, could you
please post some references as to where they occur.
Cheers,
David.
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