Abstract: A pivot assembly for a guide or marking tool (10) comprising a stock (12) with a reference edge (31) alignable with a desired datum (36), a blade (13) with a sighting, guiding or marking edge (16) and a semi-circular segment (18) provided with angle indicia (19). The stock (12) is pivotally connected to the blade (13) so that the angle between the reference edge (31) and the sighting edge (16) may be adjusted to a predetermined setting and the pivot axis (9) of the stock (12) relative to the blade (13) is located at the intersection between the reference edge (31) and the sighting edge (16) at all relative angular settings between the stock (12) and the blade (13). Pivoting of the stock and blade is effectuated by arcuate guide tracks on the stock (12) mating with corresponding depending flanges on the undersurface of segment (18).