SetUnitSystem Subroutine

  subroutine SetUnitSystem(UnitSystem)
  !+ Set the system of units to use (SI or IP).
  !+ Notes: this function *HAS TO BE CALLED* before the library can be used

    integer, intent(in)    :: UnitSystem
    !+ Units: string indicating the system of units chosen (SI or IP)

    if (.not. (UnitSystem == SI .or. UnitSystem == IP)) then
      error stop "The system of units has to be either SI or IP."
    end if

    PSYCHROLIB_UNITS = UnitSystem

    ! Define tolerance on temperature calculations
    ! The tolerance is the same in IP and SI
    if (UnitSystem == IP) then
      PSYCHROLIB_TOLERANCE = 0.001 * 9.0 / 5.0
    else
      PSYCHROLIB_TOLERANCE = 0.001
    end if
  end subroutine SetUnitSystem