All values are given in the SI system (Systeme International d'unites). Please, have a look on http://www.tcaep.co.uk/science/siunits, and Bureau International des Poids et Mesures respectively. The use of other systems of units is free to second party programs, of course.
There are only very few exceptions, e.g. if otherwise very big numbers are to be written (see <timezone> — it wouldn't make any advantage to use the unit seconds in this case).
The units are:
Length — Meter [m]
Mass — Kilogram [kg]
Volume — Cubic meter [m3]
Density — Kilogram per cubic meter [kg/m3]
Pressure — Pascal [Pa = N/m2]
Temperature — Kelvin [K]
Time — Seconds [s]
Conversions:
1 m = 39.370079 inch = 3.280840 ft
1 kg = 10-3 Tons = 2.204623 pound = 35.273962 ounce
1 m3 = 1000 Litres = 35.314667 ft3
1 kg/m3 = 10-3 Tons/m3 = 0.036127 ⋅ 10-3 pound / cubic inch
1 dyne = 10-5 N = 10-5 kg ⋅ m / s2
33.0 fsw = 1 atm = 101,325 kPa = 760 mmHg = 760 Torr
1 Pa = 1 N / m2 = 0.0101325 ⋅ 10-3 bar = 0.145038 ⋅ 10-3 psi
xK = x - 273.15 °C = x ⋅ 1.8 - 459.67 °F