This figure shows the location of a WLM box on the backing structure of an OVRO 10.4 m antenna. The WLM boxes look at the secondary using an off axis ellipsoidal mirror ("kickout"). The kickout produces a beam on the sky that is offset by only 10 arcminutes from the astronomical beam. This corresponds to a 10 meter offset at a distance of 4 kilometers, and insures that most of the water vapor in the atmosphere is seen in common between the WLM box and the OVRO antenna.