Post by CliffWhoops !!
The first reply got sent unfinished ....
To continue .....
Post by GeoffPost by CliffWhich part of the scribe lines of your micrometers and calipers do you
use?
How many angstroms am I measuring?
Angstrom... an obsolete unit of measurement. All you know is what you
read on the web, isn't it? It appears you haven't read enough.
Angstroms are indeed very much in use and in no way "obsolete".
Perhaps you should consider a bit more <G>.
Sure. Considered.
Federal Standard 376-B, January 27, 1993; page 5
http://ts.nist.gov/ts/htdocs/200/202/fs376-b.pdf
"4.3.2 Deprecated Names or Symbols. Other units from older versions of
the
metric system and metric jargon that shall not be used include:
Incorrect term Correct Unit
kilo kilogram
are square dekameter
candle or
candlepower candela
fermi femtometer
gamma nanotesla
micron micrometer
millimicron nanometer
mho siemens
ã microgram
ë cubic millimeter or microliter
4.3.3 Miscellaneous Non-SI Units Not to be Used. Additional units
that are not accepted for use include the following:
angstrom
calorie
g as a unit of acceleration (g = 9.81 m/s2)
grade or gon [1 grade = (Î/200) rad]
kilogram-force
langley (1 langley = 1 cal/cm2)
metric carat
metric horsepower
millimeter of mercury
millimeter, centimeter, or meter of water
standard atmosphere (101.325 kPa)
technical atmosphere (98.0665 kPa)
torr (133.322 Pa)"
Post by Cliffhttp://www.sizes.com/units/angstrom.htm
[
In 1978 the CIPM listed the ångström among those units acceptable to
be used with SI until the CIPM considers their use no longer
necessary. However, these units should not be introduced where they
are not used at present.2 In the same period, the American National
Standard for Metric Practice (Z210.1) also discouraged use of the
ångström.
In spectroscopy, the ångström has been displaced by the nanometer.
However, it continues to be used in various technical fields.
] ?
Post by GeoffPost by CliffTell me how many parts-per million are you uncertain about when you
measure a 100 mm dimension object with a 50-100mm mic of .01 mm
precision and how much the width of the scribe marks on the micrometer
dial affects the uncertainty of your measurement? How much does this
measurement uncertainty affect the accuracy of your part?
What was the accuracy & repeatability of that scribed meter
supposed to be? How certain are you?
Non-responsive. You didn't answer my questions
Which were immaterial to the matter under discussion,
just as chains or national parks would be.
Post by Geoffwhy do you expect me to
answer yours? You don't know the answer to that question yourself.
Well, as there are 10**10 angstroms to a meter and a meter was
defined to be 1650763.73 wavelengths of orange-red light
(corresponding to the transition between levels 2p10 and 5d5) in
the spectrum of the element krypton 86 .....
This is the old standard. The NIST states the history of the standard
and the new definition of the meter:
"2.1.1.1 Unit of length (meter) The 1889 definition of the meter,
based upon the international prototype of platinum-iridium, was
replaced by the 11th CGPM (1960) using a definition based upon a
wavelength of krypton 86 radiation. This definition was adopted in
order to improve the accuracy with which the meter may be realized.
This was replaced in 1983 by the 17th CGPM (Resolution 1; CR, 97 and
Metrologia, 1984, 20, 25):
The meter is the length of the path travelled by light in vacuum
during a time interval of 1/299 792 458 of a second.
Note that the effect of this definition is to fix the speed of light
at exactly 299 792 458 m/s. The original international prototype of
the meter, which was sanctioned by the 1st CGPM in 1889 (CR, 34-38),
is still kept at the BIPM under conditions specified in 1889."
See http://physics.nist.gov/Pubs/SP330/sp330.pdf, page 5.
Now, since the length of the meter is a function of time, we need a
proper definition of a second.
"2.1.1.3 Unit of time (second)
The unit of time, the second, was at one time considered to be the
fraction 1/86 400 of the mean solar day. The exact definition of "mean
solar day" was based on astronomical theories. However, measurement
showed that irregularities in the rotation of the Earth could not be
taken into account by the theory and have the effect that this
definition does not allow the required accuracy to be achieved. In
order to define the unit of time more precisely, the 11th CGPM (1960;
CR, 86) adopted a definition given by the International Astronomical
Union which was based on the tropical year. Experimental work,
however, had already shown that an atomic standard of time interval,
based on a transition between two energy levels of an atom or a
molecule, could be realized and reproduced much more precisely.
Considering that a very precise definition of the unit of time is
indispensable for the International System, the 13th CGPM
(1967-1968, Resolution 1; CR, 103 and Metrologia, 1968, 4, 43)
replaced the definition of the second with the following:
The second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of
the ground state of the cesium 133 atom.
At its 1997 meeting, the CIPM affirmed that:
This definition refers to a cesium atom at rest at a
temperature of 0 K.
This note was intended to make it clear that the definition of the SI
second is based on a Cs atom unperturbed by black-body radiation, that
is, in an environment whose temperature is 0 K, and that the
frequencies of primary frequency standards should therefore be
corrected for the shift due to ambient radiation, as stated at the
meeting of the CCTF in 1999."
ibid. http://physics.nist.gov/Pubs/SP330/sp330.pdf, page 6.