Abstract: The present invention relates to a device for locking in a set position along arched tape (5) preferably intended for measuring and marking. The tape is guided in a trough-shaped member (10) constituting one part of a locking mechanism and in which the tape is oriented with its convex side facing away from the bottom of the member. An elastically deformable locking member (17) constituting a second part of said locking mechanism has a part (16) displaceably disposed in a direction towards and away from the convex side of the tape guided in the trough. When the locking means is enabled, the part (16) has a radius of curvature substantially corresponding to that of the arched tape, and this radius of curvature may be different from the radius of curvature of the tape in the disabled state. The thin edges of the tape (5) will thus be urged against the corners of the trough, whereby an effective lock is obtained between the tape and the trough-shaped member in the region of the elastically deformable tape.