Compounds of Formula ; in salt or zwitterionic form wherein R1, R2, R3 and R4 have the meanings as indicated in the specification, are useful for treating conditions that are mediated by the muscarinic M3 receptor, especially inflammatory or obstructive airways diseases. The tool retaining mechanism includes a tool support member having a receiving recess detachably receiving the shank of the tool holder, a tool clamp member disposed to be displaceable with respect to the tool support member between an operative position and an inoperative position, and a mounting member detachably mounting the tool support member and the tool clamp member to the spindle. A controller tilts the MEMS mirror in response to a sensed temperature change of the arrayed waveguide grating, thereby lessening a sensitivity of the arrayed waveguide grating to the temperature change.