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WHT is an alt-azimuth telescope with overall pointing accuracy better than 1.5 arcsec (provided the telescope model for the relevant focal position has been updated sufficiently recently). The optics support structure is mechanically decoupled from the coarser mechanical structure (`Nasmyth platform') used for electronic cabinets, handling equipment, and personnel. WHT Nasmyth instruments are mounted on `instrument support pads', which form part of the optics support structure of the telescope.
UES, its camera and detector, and the dedicated A&G, are all mounted on an optical table, which is kinematically supported on a steel frame, which in its turn is rigidly bolted to the instrument support pads (steel on steel, no thermal effects). The fixed point of the 3-point kinematic support is below the UES slit. The image derotator is also, but separately, connected to the WHT optics support structure. These arrangements ensure that the whole optical system can perform operationally as a single system, to the limits of the design of its constituent parts; the observer merely verifies that WHT delivers a good image to the slit and can take for granted that UES turns that image into a spectrum which the detector and subsequent computers record for posterity.
All the electronics, and (for the time being) the temperature control unit, are mounted on the `Nasmyth platform'; this arrangement isolates the optics from vibrations such as produced by the temperature control unit. The optical table is within a constant-temperature enclosure, to obtain sufficiently stable conditions for proper operation of the spectrograph (cf. the traditional Coudé room for older high-resolution spectrographs). The camera, detector and the A&G unit are outside the constant temperature enclosure, for reasons of accessibility, but are supported by the optical table through the walls of the enclosure. Where necessary, invar has been used in the camera and A&G unit, to preserve mechanical fidelity under slowly-drifting ambient temperature.
The UES thermal enclosure and the calibration light facility of the A&G have slacker tolerances on positional stability and are bolted to the support frame, i.e. are more or less directly supported by the instrument support pads.