Abstract: An apparatus for measuring the plumbness of vertical studs of building structure frames includes a vertical main body member with a horizontal vial therein and having first and second opposed, plane, parallel surfaces, first and second vertical extension members being connected to said main body member and slidably engaging said first and second plane, parallel surfaces, respectively, first and second quick-release mechanisms releasably locking said first and second vertical extension members to said main body member, a first offset member connected to the upper end of the first vertical extension member and extending to an imaginary plane that is parallel to the first surface, and a second offset member extending from the bottom of the second vertical extension member to the imaginary plane.