Abstract: A positioning device with a pivotable positioning member. The positioning member comprises a guide lug spaced from and parallel to its pivot axis, the guide lug having a head portion which may be introduced into an enlarged end of a guideway in a support but which maintains the positioning member parallel to the pivot axis. An abutment prevents the guide lug from re-entering the enlarged end of the guideway. A strip integrally formed with the positioning member has a protruding portion which bears against one side of the support tensioning the strip. The pivotal mounting is afforded by co-operable detents including a pivot pin (e.g. on the support) with a tapered end which snaps into an aperture defined by a pair of integrally formed flexible strips (e.g. on the positioning member). The oblong aperture permits the pivot pin to shift therein as the pointer at the other end of the positioning member undergoes substantially rectilinear displacement.