popid_definition_primary_unit="Primary Unit û the main unit in the category. All conversion factors are specified in relation to this main unit. The primary units are as follows:\n\r\n\rCategory\tPrimary Unit\n\rLength\tMetres\n\rMass \tKilograms\n\rVolume\tLitres\n\rArea\t\tSquare Metres\n\rDensity\tKilograms per Litre\n\rPressure\tPascals\n\rSpeed\tMetres per Second\n\rEnergy\tJoules\n\rForce\t\tNewtons\n\rPower\tWatts\n\rTemperature\tCelcius\n\r\n\rThe choice of primary unit has been derived from the System InternationalΘ standards (SI units), with the exception of Temperature where Celcius seemed a more logical choice than Kelvin."
