The present Monograph is based on an earlier Memorandum produced bythe Directorate of Ordnance Factories (Explosives) for the use, primarily, ofthose concerned with pilot plant and plant scale experiments on chemical manufacturingprocesses in the Royal Ordnance Factories (Explosives). Much workof this type was being carried out and it had become evident that it was desirablefor the results of such experiments to be subjected to critical tests of significance.A convenient account of the straightforward tests of significance, written fromthe point of view of the individual who has to apply them in practice withoutnecessarily a full knowledge of their theoretical background, was not readilyavailable, and an attempt was therefore made to prepare one.It was evident that to apply tests of significance conveniently and economicallythe experiments had to be planned in appropriate forms. It is considered thatthe methods outlined should be as much a standard tool of the industrial experimenteras a chemical balance is of the laboratory experimenter. In carrying outan industrial experiment the choice is not between using a statistical design withthe application of the appropriate tests of significance or the ordinary methods:the choice is between correct or incorrect methods. Even the simplest experimentrequires an estimate of the significance of its results.The practice sometimes followed of consulting the statistician only after theexperiment is completed and asking him "what he can make of the results" cannotbe too strongly condemned. It is essential to have the experiment in a formsuitable for analysis and in general this can only be attained by designing theexperiment in consultation with the statistician, or with due regard to thestatistical principles involved.The present Monograph, therefore, is intended to be a guide to both theplanning and the interpretation of experiments on the industrial scale, and it ishoped that the methods described will become part of the everyday techniqueto those who carry out such experiments.R. C. BOWDEN,Director of Ordnance Factories (Explosives)Ministry of Supply