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draughtsman. In some the stock is rectangular in section, and the blade morticed into it, as in Fig. 1. In others the blade is dovetailed and let into the stock for the whole of its thickness, as in Fig. 2 ; or morticed, as in Fig. 1, but fitted with a tongue-piece the length of the stock, as in Fig. 3. Neither of these plans is to be recommended ; they involve unnecessary work and care in fitting during their manu- facture, are more liable to get damaged in their usage, and are practically imperfect as a tee-square in some of its essential require- ments. To be perfect in construction, a tee-square should be as light as is consistent with its necessary strength and stiffness of parts ; it should be made of suitable material, easily manufactured, put together, and repaired, and withal as truly correct as it is possible to be made. Such a square is represented in Fig. 4 ; it has a taper blade, which is generally about double the width where secured to the stock as it is at the tip. Its tapering form serves two purposes, the primary one being that'it adds strength and stiffness to the blade and prevents its buck- ling a common fault with all parallel-bladed squares and the other, its excess of width at the stock, prevents it from rocking, and gives amjAe room for securing it to the stock. The blade is also easily and correctly fitted to the stock, and has also one great advantage over all the others in that the set-squares used with it are far more easily manip- ulated than is possible with any of the three previously referred to. 3. In cases where many parallel lines have to be drawn, of lengths beyond the capabilities of ordinary set-squares, and in directions other than square with, or parallel to, the working edge of the drawing- board, it is convenient to have for use an adjits'able-bladed tee-square, or one whose blade can be set at any desired angle. The blade of such