JCMT Pointing Model - Parameter 4

The amount by which the telescope beam is not perpendicular to the elevation axis.

In the following diagram :

A, A' indicate the directions of the ideal and real telescope beams.
A star at real azimuth a has apparent azimuth a' , so the change in azimuth is   a' - a = -theta.

Any misalignment of the beam in the elevation direction is incorporated into the elevation zero-point.