An engineers square is an all metal square, consisting of a blade and stock (similar to a carpenters try square) and usually silver soldered together. The stock is thicker than the blade, allowing the stock to be placed against an edge in order to mark a right angle, and also to make it more stable if its stood with the blade facing upwards.Engineers squares are usually manufactured to a high degree or accuracy, and often used to check and calibrate machinery. If extreme accuracy is important, buy one with a stated tolerance.