[en] The calculation of material buckling in a cold critical assembly is considered in detail. The technique is extremely simple, permitting rapid calculation without computers. Long intricate calculations, involving many minor effects that are difficult to assess, are not always justified, if only because of lack of accuracy in the physical constants. If certain effects become significant they can always be individually computed. It is admittedly not easy to decide which effects must be considered and which can be ignored. Hence, the importance we attach to the theoretical study of effects which are difficult to assess, aiming at simple, easily-understood formulae for their calculation which will clearly reflect their physical characteristics. 14 refs, 7 tabs