Specify the measured gravitational flexure of the feed tower.

Arguments:

Double flexure

Example:

The following example tells the control system that to point at a topocentric elevation of el degrees, it must actually point the telescope encoders 0.00667 * cos(el) degrees higher in elevation, to correct for the sag of the feed.

  cal_flexure 0.00667

Context:

The telescope dish and feed supports deform under gravity as a function of elevation. To first order, the prime focus sags by an amount proportional to the cosine of the target elevation of the telescope. So to point the feed at a given target elevation, one must make the telescope encoders read this much higher than the target elevation.