Green Grass Group's DoubleVsquare ($25) — which consists of two triangular-type aluminum squares hinged down the center — makes it easier to transfer marks around corners, from the sharpest acute angles to nearly flat facets. Open, it works well for jobs like marking out siding across outside or inside corners or as a saddle square to mark two sides of a deck post. Closed, it works just like a standard triangular square. The slight play in the hinge keeps it from being a high-precision tool, but it's fine for most construction purposes. Other good uses include marking square across waney 2-bys that don't have sharply defined edges and guiding a long drill bit along the open hinge to drill straighter into concrete or thick timbers. 800-951-9541,