WP-34S galUS-> l Precision

[Nigel (UK)]

(11-27-2016 03:12 PM)Dieter Wrote:  

(09-07-2016 10:20 PM)Nick Wrote:  The US Gallon has an exact value of 3.785411784 per:

1 yd (36 in) = 0.9144 m [international definition]
1 gal = 231 in^3 [US definition]

If that's accurate, can the precision be increased?

By simply changing the respective constant in the 34s source code. Technically this should be no problem at all. A source for the correct constant should not be hard to find. If everything else fails: HP correctly implements 3,785411784 l/gal in their calculators. I imagine my 35s is not the only one that does so. And, honestly, I think the 34s should be at least on par with it. ;-) So I agree it's time for a new build.

Dieter

Here's the source code containing the conversion constants: it's in the file compile_consts.c .

Code:


/* Imperial/metric conversions.
 * Data taken from http://physics.nist.gov/Pubs/SP811/appenB9.html
 * In general, the values are rounded to 6 or 7 digits even though
 * more accurate values are known for many of these.
 */
struct _constsml conversions[] = {
    CONV("kg",    "lb",        "KG_LBM",    "0.4535924"),        // source: NIST
    CONV("kg",    "stone",    "KG_STONE",    "6.3502936"),        // derived: 14 lbs to a stone
    CONV("kg",    "cwt",        "KG_CWT",    "50.8023488"),        // derived: 112lb to a long cwt
    CONV("kg",    "s.cwt",    "KG_SHCWT",    "45.35924"),        // source: NIST hundredweight, short 100lb
    CONV("g",    "oz",        "G_OZ",        "28.34952"),        // source: NIST
    CONV("g",    "tr.oz",    "G_TOZ",    "31.10348"),        // source: NIST
    CONV("l",    "galUK",    "L_GALUK",    "4.54609"),        // source: NIST
    CONV("l",    "galUS",    "L_GALUS",    "3.785412"),        // source: NIST
    CONV("l",    "cft",        "L_CUBFT",    "28.31685"),        // source: NIST
    CONV("ml",    "flozUK",    "ML_FLOZUK",    "28.41306"),        // source: NIST oz UK fluid
    CONV("ml",    "flozUS",    "ML_FLOZUS",    "29.57353"),        // source: NIST oz US fluid
    CONV("cm",    "inches",    "CM_INCH",    "2.54"),        // source: NIST
    CONV("m",    "fathom",    "M_FATHOM",    "1.8288"),        // derived: 6 feet
    CONV("m",    "feet",        "M_FEET",    "0.3048"),        // source: NIST
    CONV("m",    "feetUS",    "M_FEETUS",    "0.3048006096"),        // source: Wikipedia etc
    CONV("m",    "yards",    "M_YARD",    "0.9144"),        // source: NIST
    CONV("km",    "miles",    "KM_MILE",    "1.609344"),        // source: NIST
    CONV("km",    "l.y.",        "KM_LY",    "9.4607304725808E12"),        // source: IAU (see http://www.hpmuseum.org/forum/thread-2262.html)
    CONV("km",    "pc",        "KM_PC",    "3.085678E13"),        // source: NIST
    CONV("km",    "AU",        "KM_AU",    "149597900"),        // source: NIST, IAU 2009 gives 1.49597870700E11
    CONV("km",    "nmi",        "KM_NMI",    "1.852"),        // source: NIST
//    CONV("m\232",    "square",    "M_SQUARE",    "9.290304"),        // derived: 
//    CONV("m\232",    "perch",    "M_PERCH",    "25.29285264"),        // derived: 
    CONV("ha",    "acres",    "HA_ACREUK",    "0.40468564224"),    // derived: 43560 square feet
    CONV("ha",    "acreUS",    "HA_ACREUS",    "0.4046873"),        // source: NIST
    CONV("N",    "lbf",        "N_LBF",    "4.448222"),        // source: NIST
    CONV("J",    "Btu",        "J_BTU",    "1055.056"),        // source: NIST BTUit
    CONV("J",    "cal",        "J_CAL",    "4.1868"),        // source: NIST calorie it
    CONV("J",    "kWh",        "J_kWh",    "3600000"),        // source: NIST
    CONV("Pa",    "atm",        "Pa_ATM",    "101325"),        // source: NIST atmosphere standard
    CONV("Pa",    "bar",        "Pa_bar",    "100000"),        // source: NIST
    CONV("Pa",    "mmHg",        "Pa_mmHg",    "133.3224"),        // source: NIST cm mercury conventional
    CONV("Pa",    "psi",        "Pa_psi",    "6894.757"),        // source: NIST pound-force per square inch
    CONV("Pa",    "inHg",        "Pa_inhg",    "3386.389"),        // source: NIST inch of mercury conventional
    CONV("Pa",    "torr",        "Pa_torr",    "133.3224"),        // source: NIST
    CONV("W",    "hp(I)",    "W_HP550",    "745.6999"),        // source: NIST horsepower 550 ft . lb / s
    CONV("W",    "hp(M)",    "W_HP",        "735.4988"),        // source: NIST horsepower metric
    CONV("W",    "hp(E)",    "W_HPe",    "746"),            // source: NIST horsepower electric
    CONV("t",    "tons",        "T_TON",    "1.016047"),        // source: NIST ton, long 2240lb
    CONV("t",    "s.tons",    "T_SHTON",    "0.9071847"),        // source: NIST ton, short 2000lb

    CONV(NULL, NULL, NULL, NULL)
};

This code is processed to give single-precision (about 16 sf) conversion factors; there's no support in the code as it stands for double precision, but this shouldn't really be a problem.

What changes to the constants in this code would people like to see? If the changes are properly sourced perhaps Paul would replace the code above with the new improved version; if not, I could include the new code as a compile-time option and build a version of the firmware using it.

Nigel (UK)