the underlying psychrometric parameter data for the psychrometric chart and the mollier diagram are identical. at first glance there is little resemblance between the charts, but if the chart is rotated by ninety degrees and looked at in a mirror the resemblance becomes apparent. the mollier diagram coordinates are enthalpy and humidity ratio. the enthalpy coordinate is "skewed" and the lines of constant enthalpy are parallel and evenly spaced. the ashrae psychrometric charts since 1961 use similar plotting coordinates. some psychrometric charts use "dry-bulb temperature" and "humidity ratio" coordinates.