The calculations within Psyclone generally use ideal gas equations to emulate UK and USA psychrometric charts as closely as possible. However, small differences (generally less than 1%) will occur as the charts are based on the formulas of Goff & Gratch and Hyland & Wexler rather than the ideal gas equations.
The USA metric and UK (metric) psychrometric charts are very similar. However, the USA/UK metric charts and USA imperial charts express significantly different values for specific enthalpy. This is because specific enthalpy is measured above an arbitrary zero point and different points are used for the two charts. The differences have little effect on calculated coil duties, etc.
Within Psyclone, increases in sensible temperature (heating) or moisture content/humidity ratio are defined as +ve loads; decreases in sensible temperature (cooling) or moisture content/humidity ratio are defined as -ve loads