Following this, in the middle pane we consider the case of assuming ∆H vap / (R∆Z vap ) is constant. For the value of ∆H vap / (R∆Z vap ) we compare use of the value at the lowest temperature (the triple point, min), the average value (avg) and the average (natural) log value (Lavg), and the value at the highest temperature (0.097 K below the critical point, max). We find that the use of the average and average log value result in excellent predictions that appear to overlap the reference data. The use of the value at the highest temperature also performs exceptionally well. The performance with the minimum temperature is the worst; nonetheless, the predictions are still very good considering they require only knowledge of ∆H vap / (R∆Z vap ) at the triple point.