Chart entitled 'The 1939 Heat-Entropy Diagram for Steam' Plotted from the 1939 Callendar Steam Tables. Based on Research by Prof A. C. Egerton F.R.S. & Mr G. S. Callendar. Published by Edward Arnold & Co London for the British Electrical & Allied Industries Research Association. Printed coloured chart plotting the value of the tables in 'The 1939 Callendar Steam Table'.