Here are the proposed changes to CONVERT. (Editor: This includes citations for some non-obvious values, if you need to change the citation format feel free. None of these citations are normative.)

In row "ly" (light-year), append this to the Description:

, exactly (299792458 m/s) (3600 s/hr) (24 hr/day) (365.25 day).

(Source: International Astronomical Union (IAU),

"Measuring the Universe: The IAU and astronomical units",

http://www.iau.org/public/measuring/).

In row "bushel", append this to the Description:

, exactly 2150.42 cubic international inches.

(Source:

National Institute of Standards and Technology (NIST),

Appendix C of NIST Handbook 44, "Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices",

http://ts.nist.gov/WeightsAndMeasures/Publications/appxc.cfm)
In row "parsec" or "pc", append this to the Description:

, exactly AU/tan(1/3600 degree) where an AU is exactly 149,597,870.691 kilometers.

(Source: International Astronomical Union (IAU),

"Measuring the Universe: The IAU and astronomical units",

http://www.iau.org/public/measuring/).

A parsec is approximately 3.085677581E+16 m.

In row "HP" (horsepower), REPLACE the old Description:

Horsepower. The unit "h" is deprecated and should be replaced with "HP".

with this Description:

Mechanical horsepower aka Imperial horsepower.

Exactly 550 foot-pounds per second.

(SOURCE:

National Institute of Standards and Technology (NIST),

"The NIST Guide for the Use of the International System of Units", section B.9,

http://physics.nist.gov/Pubs/SP811/appenB9.html).

A horsepower is approximately 745.699871582 W.

("Unit Conversion Utility",

http://www.metas.ch/metasweb/Themen/Masseinheiten/calculation/en_calculation_frame_umrechnungen.html)
The unit "h" is deprecated and should be replaced with "HP".

{NOTE: Wikipedia has a better description of horsepower, and we could cite a specific dated version, but some

people have a Wikipedia allergy so I'm not citing

http://en.wikipedia.org/wiki/Horsepower even though it is

a far better source of information.).

In row "PS" (horsepower), append this to the Description:

, the amount of power to lift a mass of 75 kilograms in one second against the earth gravitation between a distance of one meter, approximately 735.49875 W

(SOURCE: "Die gesetzlichen Einheiten in Deutschland"

http://www.ptb.de/de/publikationen/download/pdf/einheiten.pdf ).

{I can't read German, but I think this is accurate. Again, the Wikipedia article is more substantive:

http://en.wikipedia.org/wiki/Horsepower
but Wikipedia then cites this German document, so I'm trying to cite the authoritative source.}

In row "uk_gal" (UK/Imperial gallon), append this to the Description:

, 4.54609 liters.

{I'm having trouble getting an authoritative source, so let's

just use this. This can be computed from the existing text.

This page:

http://en.wikipedia.org/wiki/Imperial_units
claims that "The Weights and Measures Act of 1985 switched to a gallon of exactly 4.54609 l"

Unfortunately, later versions have removed that definition, so I didn't find its definition here:

http://www.statutelaw.gov.uk/content.aspx?activeTextDocId=2191980
}

In row "uk_qt" (UK/Imperial quart), append this to the Description:

, exactly 1/4 of a UK gallon.

In row "uk_pt" (UK/Imperial pint), append this to the Description:

, exactly 1/8 of a UK gallon.

In row "pond", append this to the Description:

, 9.80665E-3 N.

{The most complete source of information on "pond" that I found was:

http://en.wikipedia.org/wiki/Kilopond - I'm sure there are better sources, please assist if you can. However, this is completely consistent with the OOo value of "pond", where 1 N = 101.9716 pond, so I take this as confirmed.

This is consistent with the official value of the Earth's gravitational force as defined by the third CGPM (1901, CR 70) definition of standard gravity, gn=9.80665 m/s2.}

After the end of the first table in CONVERT, state:

"If a conversion factor (as listed above) is not exact, an implementation may use a more accurate conversion factor instead."

Also, in the first table (listing the function arguments) add the following sentence to the Description for to-unit and from-unit. "Additionally, unit names containing a 'FULL STOP' (U+002E) character may be used for implement-defined units"

In row "gal" (Gallon (U.S. customary liquid measure)), append this to the Description:

, 3.785411784 liters.

(299 792 458 m/s) (3600 s/hr) (24 hr/day) (365.25 day/year)

1 bushel = 2150.42 cubic inches exactly.

SOURCE:

"Appendix C of NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices"

http://ts.nist.gov/WeightsAndMeasures/Publications/appxc.cfm

[Bushel is often used for weight, too, but we're only using them for volume.]

The NIST document has some other traditional measurement notes.

Hope that helps.

OTHER NOTES:

CIA notes that 1 U.S. bushel = 32 dry quarts.

(https://www.cia.gov/library/publications/the-world-factbook/appendix/appendix-g.html).

The term "pc" (parsec) overrides "pico-calorie". That's not a problem in any way, it's just a ramification of the rules and I thought I'd point that out.