Abstract: A right-angle index device comprising two unextensible tapes having hook means at one free end, a first mechanism for withdrawing said both tapes by the same length under controlled conditions, a second mechanism for stopping said first mechanism to fix the length of said both tapes at the desired value, a take-up mechanism for rolling up said both tapes through said first and second mechanisms, to which the other ends of said both tapes are fixed, and casing means for accommodating therein said first and second mechanisms and said take-up mechanism and allowing said both tapes to be rolled around said take-up mechanism for withdrawal.