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HISTORY AND CONSTRUCTION] results given by various formulas. These often vary considerably, so in order that a direct comparison in the tables may be made, this value is obtained for wrought iron plate only, using Tresidder’s formula, which is one of the most trustworthy. The equivalent thickness of Krupp cemented steel armour can be obtained immediately by dividing the tabulated value for wrought iron by a “factor of effect” of 2·3 to 2·4 for uncapped armour piercing

shot, and about 2·0 for capped armour piercing shell. These factors are dependent on the nature of the projectile and must therefore be taken as approximate.

Tables VIII.-XXII. are obtained from trustworthy sources, but as great secrecy is now observed in many countries there may be a few inaccuracies; in some cases the whole of the data are not available.