For use in establishing the prescribed elevation difference between an adjustably movable deck member and a relatively stationary support member, an elevation gauge comprising a case, a float disposed in the case and guided for vertical movement, a lead screw for moving the float, a scale carried by the float to extend vertically upwardly and to cooperate with an indicator pointer carried by the case to indicated lower selected vertical position of the float, a second float guided for vertical movement on the case, and a signal device for providing an output when the second float is in a preselected elevational position relative to the first float. The signal device cooperates between the floats, and the case is adapted to rest on one of the members while the said second float is adapted to rest on the other of said members. A plurality of bolt assemblies is provided for adjustably supporting the deck member on the support member. Each bolt assembly comprises a vertically extending bolt, a hanger for mounting on the support member, with the upper end of the bolt penetrating through the hanger and being rotatable relative to the hanger. A first nut threadedly engages the upper end of the bolt and restrains the bolt against movement downwardly relative to the hanger. A second nut threadedly engages the bolt and supports the deck member, the second nut being prevented from rotating when the bolt rotates. The first nut and the upper end of the bolt are proportioned and designed to be engaged by a tool and rotated together relative to the hanger to raise and lower the deck member to the prescribed height determined by the said gauge.