Keep a 12-in. combo square and a 4-in. double square near your workbench and you'll find you reach for them often, whether you are measuring and laying out parts, checking to see if surfaces are flat and square, fitting dovetails, tuning up power tools, or performing any of an infinite number of other layout and setup tasks. So Phil Lowe did a head-to-head test of both types of squares, narrowing his choices to models that passed an accuracy test and had features that are most useful to woodworkers. He scored them for accuracy, ease of use, and readability. Tested were 12-in. combo squares from General, iGaging, Johnson, Mitutoyo, Products Engineering Corp. (PEC), Starrett, and Swiss Precision Instruments (SPI), and 4-in. double squares from iGaging, PEC, Starrett, and SPI.

From Fine Woodworking #229