The first source of photometric standard stars is the Landolt faint star catalogue (1992, AJ, 104, 340), which contains over 500 stars centered on the celestial equator with UBVRI photoelectric observations. The majority of Landolt stars have 11.5 < V < 16.0 and -0.3 < (B-V) < 2.3. Data (positions, magnitudes, and colors) and finding charts for this catalogue can be found in two green binders in the WHT control room. This catalogue has also been loaded into the WHT system computer, and can be accessed automatically by typing GOCAT followed by the object name (e.g. 92-309). The UBV photometry is tied to the Johnson & Morgan (1953) system, while the RI photometry is based on the Cousins (1976) system, which was derived from the Kron et al (1953) data. Some of these fields contain several stars which will all fit in the WHT prime focus field.
A few words of warning are in order. First, many of the Landolt stars have only been observed once or twice, and may not be suitable for very high-precision photometry. Second, some of these stars have large proper motions; proper motions where known are given in the green binder. Finally, only the faintest Landolt standards should be used (14 V 16) at the WHT prime focus, since stars brighter than this will saturate in only a few seconds, especially in R and I.