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# TCX Unit Conversion Library

, 1 Dec 1999
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This library offers functions to convert values between units of measurement. It's very simple to use. For example, to convert between mph (miles per hour) to m/s (meters per second), just use the following code:

```double dValue = 1.0;
TcxConvertUnit( dValue, _T("mph"), _T("m/s") );
// <dValue> is now in "m/s"
```

The units are represented as strings, as the intention of the library is to afford unit entrance support at the UI level. In fact, the Demo Application that accompanies this article is a very simple (yet powerful) unit conversion utility.

The table of supported units is currently hard coded. You can add your own new units just following the instructions in the source file (TcxUnitConverter.cpp).

The unit interpreter accepts all the multiplication prefixes of the International System of Units (see the Appendices section).

The unit interpreter accepts also linear unit expressions. For example, you can convert from acre (Acres) to mi^2 (square miles), or from N (Newtons, the unit of strength in the International System of Units) to m*kg/s^2 (meter times kilogram per square second).

The following are samples of valid unit expressions (they are all units of strength).

• m*kg/s^2
• m*kg*s^-2
• m/kg^-1*s*s
• kg*s^-2/m^-1

There can be only one division ('/') symbol in the expression, and all right terms are considered as part of the denominator (e.g. m/s^2 equals m/s*s). Parenthesis are not used. Exponents, when applicable, must be positive or negative literal integers.

 This source code is provided "as is" without express or implied warranty. Use it at your own risk! While I have made every effort to remove any undesirable "bugs", I cannot be held responsible if it causes any damage or loss of time, data, or Martian probes.

### Known Limitations

The unit converter can only perform the following type of conversion:

```Unit1 = K * Unit2;  // K is a floating point constant
```

This is valid for the greatest multitude of the common day units we can think of, but for temperature units.

Temperature units as Kelvin, Celsius and Fahrenheits all demand conversion formulas in the following form:

```Unit1 = K * Unit2 + K0;  // K and K0 are floating point constants
```

The library will still convert between these units, but, in this case, the value is supposed to be a temperature variation rather than an absolute temperature.

### Things to do

• Implement UI Controls that automatically make use of these features.
• Implement a more flexible Unit Converter so sets of units can be "loaded" and combined in runtime.

### Using the Demo Application

In the From/Value field, enter the source value you want to convert. In the From/Unit field, type the unit of the source value, or choose one from the dropdown list. In the To/Unit field, type the target unit or choose one from the dropdown list. The result will be displayed in the To/Result just-in-time. You can select & copy from this field.

To enter unit expression in either the From/Unit or the To/Unit fields, you must type them. The dropdown lists show only sigle units.

### Appendices

Table 1: Multiplication prefixes of the International System of Units

PrefixNameConstant
YYotta1e+24
ZZetta1e+21
EExa1e+18
PPeta1e+15
TTera1e+12
GGiga1e+9
MMega1e+6
k or Kkilo1e+3
h or Hhecto1e+2
DDeka1e+1
ddeci1e-1
ccent1e-2
mmili1e-3
u or µmicro1e-6
nnano1e-9
ppico1e-12
ffemto1e-15
aatto1e-18
zzepto1e-21
yyocto1e-24

Table 2: Basic Units

AbbrTag
AAmpere
KKelvin
cdCandela
gGram
mMeter
molMole
sSecond

Table 3: Derived Units

AbbrTagDefinition
Bqbecquerel1 [l/s]
BtuInternationalTableBtu1055.05585262 [Kg*m^2/s^2]
CCoulomb1 [A*s]
CiCurie3.7*1010 [l/s]
GyGray1 [m^2/s^2]
HHenry1 [Kg*m^2/A^2*s^2]
HzHertz1 [s^-1]
JJoule1 [Kg*m^2/s^2]
KnotNauticalMilesPerHour463.0/900.0 [m/s]
NNewton1 [Kg*m/s^2]
OhmOhm1 [Kg*m^2/A^2*s^3]
OzUKUKFluidOunce2.8413075e-5 [m^3]
PPoise0.1 [Kg/m*s]
PaPascal1 [Kg/m*s]
PdlPoundal0.13825495376 [Kg*m/s^2]
PicaPica1.0/72.0 [in]
RRoentgen0.000258 [A*s/Kg]
SSiemens1 [A^2*s^3/Kg*m^2]
StStokes0.0001 [m^2/s]
SvSievert1 [m^2/s^2]
TTesla1 [Kg/A*s^2]
UUnifiedAtomicMass1.6605402e-27 [Kg]
VVolt1 [Kg*m^2/A*s^2]
WWatt1 [Kg*m^2/s^3]
WbWeber1 [Kg*m^2/A*s^2]
acreAcre4046.87260987 [m^2]
arcminArcMinute2.9088820866e-4 [r]
arcsArcSecond4.848136111e-6 [r]
atmAttmosphere101325 [Kg/m*s^2]
auAstronomicalUnit1.495979*1011 [m]
bBarn1e-28 [m^2]
barBar100000 [Kg/m*s^2]
bblBarrel0.158987294928 [m^3]
buBushel0.03523907 [m^3]
cLightSpeed299792458 [m/s]
calCalorie4.1868 [Kg*m^2/s^2]
chainChain20.1168402337 [m]
ctCarat0.0002 [Kg]
cuUSCup2.365882365e-4 [m^3]
dday86400 [s]
dynDyne0.00001 [Kg*m/s^2]
eVElectronVolt1.60217733e-19 [Kg*m^2/s^2]
ergErg0.0000001 [Kg*m^2/s^2]
fathFathom1.82880365761 [m]
fbmBoardFoot0.002359737216 [m^3]
fcFootcandle10.7639104167 [cd*sr/m^2]
fermiFermi1e-15 [m]
flamFootlambert3.42625909964 [cd/m^2]
ftInternationalFoot0.3048 [m]
ftUSSurveyFoot0.304800609601 [m]
gaStandardFreefall9.80665 [m/s^2]
galUSGallon0.003785411784 [m^3]
galUKUKGallon0.004546092 [m^3]
gfGramForce0.00980665 [Kg*m/s^2]
grainGrain0.00006479891 [Kg]
hHour3600 [s]
haHectare10000 [m^2]
hphorsepower745.699871582 [Kg*m^2/s^2]
inInch0.0254 [m]
inH2OInchesOfWater248.84 [Kg/m*s^2]
inHgInchesOfMercury3386.38815789 [Kg/m*s^2]
kipKilopoundForce4448.22161526 [Kg*m/s^2]
kphKilometersPerHour5.0/18.0 [m/s]
lLiter0.001 [m^3]
lamLambert3183.09886184 [cd/m^2]
lbAvoirdupoisPound0.45359267 [Kg]
lbfPoundForce4.44822161526 [Kg*m/s^2]
lbtTroyPound0.3732417216 [Kg]
lmLumen1 [cd*sr]
lxLux1 [cd*sr/m^2]
lyrLightYear9.46052840488*1015 [m]
mhoMho1 [A^2*s^2/Kg*m^2]
miInternationalMile1609.344 [m]
miUSUSStatuteMile1609.34721869 [m]
milMil0.0000254 [m]
minMinute60 [s]
mmHgMilimeterOfMercury133.322368421 [Kg/m*s^2]
mphMilesPerHour0.44704 [m/s]
nmiNauticalMile1852 [m]
ozOunce0.028349523125 [Kg]
ozflUSFluidOunce2.95735295625e-5 [m^3]
oztTroyOunce0.0311034768 [Kg]
pcParsec3.08567818585106 [m]
phPhot10000 [cd*sr/m^2]
pkPeck0.0088097675 [m^3]
psiPoundsPerSquareInch6894.75729317 [Kg/m*s^2]
ptPint0.000473176473 [m^3]
qtQuart0.000946352946 [m^3]
rdRod5.02921005842 [m]
remRem0.01 [m^2/s^2]
sbStilb10000 [cd/m^2]
slugSlug14.5939029372 [Kg]
stStere1 [m^3]
tMetricTon1000 [Kg]
tbspTablespoon1.47867647813e-5 [m^3]
thermEECTherm105506000 [Kg*m^2/s^2]
tonShortTon907.18474 [Kg]
tonUKUKLongTon1016.0469088 [Kg]
torrTorr133.322368421 [Kg/m^2]
tspTeaspoon4.92892159375e-6 [m^3]
ydInternationalYard0.9144 [m]
yrYear31556925.9747 [s]
°Degree1.74532925199e-2 [r]
°CDegreeCelsius1.0 [K]
°FDegreesFahrenheit1.0/1.8 [K]
°RDegreesRankine1.0/1.8 [K]
µMicron1e-6 [m]
ÅAngstrom1e-10 [m]

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