These parameters are checked and adjusted by dedicated pointing runs. The profile is measured by inclinometry and is fed into the TEL escope task as a look-up table. Elevation pointing is also corrected for refraction , calculated as a function of ambient atmospheric parameters, and for the difference in temperature between the front and back legs.
Errors increase with turbulence and rapid thermal changes.
Collimation offsets for each Front End are used in order to aid switching between FEs. The current track model is from 990516 and the latest pointing run is shown below.