In an interesting Technical Note in the January 1953 Journal, Messrs. Dickinson and Hadley reported some results from tests made to check a proposed extension to the Royal Aeronautical Society Data Sheets on stresses and deflections in flat panels subjected to normal pressure. The test rig was originally too weak and did not provide the edge conditions which were assumed when calculating the curves of Data Sheet 02.09.02. This explains the discrepancy with regard to the deflections, but it is remarkable that the measured membrane stresses f3 were so low. It is a well-known fact that the membrane tension at the centre of a square plate with large deflections is not influenced very much by different edge conditions. This can be seen in Data Sheet 02.09.05 where the two extremes, free edges and edges held apart, are represented for a square plate with edges free to rotate. The membrane tension at the edge is, of course, much more sensitive for an edge displacement, but we suppose that f3, is the membrane stress at the centre of the plate (as in Data Sheet 02.09.05).