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The Epstein square is the standard loss-measuring apparatus for electrical steel laminations tested at power frequencies. Investigations have shown that, if laminations of grain-oriented 3.25% silicon-iron are cut at various angles to the rolling direction, the apparent powerloss depends on the type of stacking used. Two types of stacking were found to give loss values close to single-strip measurements, whereas another type, and a random stacking method, gave apparent losses as much as 50% less than single-strip values. The effect is greater with betteroriented material. The main cause of the difference in apparent losses stems from the flux transfer mechanism at the corners which cause the corner loss in some cases to be less than the limbloss, thus giving artificially low apparent losses.