Abstract: An actuating mechanism is rotatably and pivotably mounted to a rotatable adjusting mechanism of an instrument. The rotatable mechanism includes a bearing surface and a friction surface. The actuating mechanism includes a pivot and friction means. By pivoting the actuating mechanism about the pivot against the bearing surface, the friction means engages the friction surface. The actuating mechanism and adjusting mechanism are thereby locked together and can be rotated in unison. The rotatable mechanism may include a second bearing surface and a second friction surface and the actuating mechanism may include a second pivot and a second friction means. The second bearing surface and the second pivot are adjacent each other, as are the second friction surface and the second friction means. Pivoting the actuating mechanism in a second direction will engage the second pivot to the second bearing surface and the second friction means to the second friction surface.