An additional effective upper limit to the altitude of the telescope of 89.8 is imposed by the speed limit in azimuth --- see Section .
The telescope is partially obscured at elevations below 12.
The area of the sky accessible to the WHT is shown in Figure .
Constraints on sky position angle depend on instrument mounting.
Pointing accuracy: rms residual of a global fit = 1.1 arcsec (Cass)
Pointing accuracy: rms residual of a global fit = 1.5 arcsec (Nasmyth)
Tracking accuracy:
(unguided) < 0.3 arcsec in 3 minutes; < 1.0 arcsec in 10 minutes
(guided) < 0.2 arcsec
Rotator tracking: < 0.2 arcsec over the whole field
Offsetting accuracy: < 0.2 arcsec over 10 arcmin