However, software can greatly aid in the analysis and handling of psychrometric data. With a conventional psych chart, the contractor must use a straight edge and pencil to plot lines and read data. The whole affair is very imprecise as the width of a pencil lead can cause significant error. In addition, most psych charts are printed for sea level barometric pressure. If a project is located thousands of feet above sea level, the standard psych chart cannot be reliably used.
Barometric pressure affects the density of air and hence, the thermodynamic properties of air.
High altitude psychrometric analysis requires a special psych chart or lengthy manual calculations. There is actually a wide range of psychrometric software available. Some of it does nothing more than list all the properties of air when given any two conditions about a single state point. Nice, but not that useful. The next level of analysis involves the ability to perform mixed air psychrometrics where two state points are defined along with corresponding cfm values.