Abstract: A linear measuring instrument for attachment to a cutting saw includes a rack and pinion gear assembly for unwinding a measuring tape coiled on a rotatable drum. The pinion gears are gear coupled with the axle of the drum, and the rack gear is manually movable for rotating the pinion gears. Therefore, upon depressing the rack gear, the tape is extendable for uniformly measuring long bolts cut from a log, for example. Spaced bearings are mounted on a housing containing the drum and the tape, the bearings being in rolling engagement with the tape during the unwinding for reducing friction between the turns as the tape unwinds, and for otherwise confining the tape within the housing. A variable limit stop arrangement is provided for limiting the extent of rack gear movement and thus limiting the extent of the tape unwound from the housing so that log bolts of different uniform lengths may be cut.