The James Clerk Maxwell Telescope is the world's largest telescope
working at wavelengths of about 1 millimetre. It is of alt-az design,
most of the load being carried on the central bearing, with about 10
of
the load borne by 4 wheels. These wheels are conic sections, rolling on
a wide track that sits atop the central plinth wall.
If the track was flat and horizontal, the telescope pointing would be
dependent only upon 7 parameters describing errors in construction and
alignment of the antenna : viz the deviation from the true vertical of
the azimuth axis (2 parameters), the
non-orthogonality of the elevation axis from the azimuth axis, and of the
telescope beam from the elevation axis, the flexure in the secondary mirror
structure, and the two encoder zero-points - (see MTUN025 : " Pointing",
and MTIN062 : " Geometry of Telescope Drives"). Even if the track was
flat and not horizontal, the additional error would be encompassed by
adjustments to the first two terms in the 7-parameter model.