A try- square is a woodworking tool used for marking and measuring a square piece of wood. The square refers to the tool's primary use of measuring the accuracy of a right angle (90 degree angle); to try a surface is to check its straightness or correspondence to an adjoining surface.
Try square is used to check right angle, not to measure.

A steel rule is exactly what it sounds like... a rule manufactured from either spring or stainless steel that feature either metric or imperial (or both) scales along its length.

For units of metric system the least count of steel rule is 0.5mm.

A try- square is a woodworking tool used for marking and measuring a square piece of wood. The square refers to the tool's primary use of measuring the accuracy of a right angle (90 degree angle); to try a surface is to check its straightness or correspondence to an adjoining surface.