A turbine map shows lines of percent corrected speed (based on a reference value) plotted against the x-axis which is pressure ratio, but deltaH/T (roughly proportional to temperature drop across the unit/component entry temperature) is also often used. The y-axis is some measure of flow, usually non-dimensional flow or corrected flow, but not actual flow. Sometimes the axes of a turbine map are transposed, to be consistent with those of a compressor map. As in this case, a companion plot, showing the variation of isentropic (i.e. adiabatic) or polytropic efficiency, is often also included.