The formula α = T _obs ΔT + a sin( φ'- δ) sec δ + b cos( φ' - δ) + c* sec δ, in which α is the right ascension of the star observed, T _obs is the time at which the star was observed to pass through the meridian, ΔT is the clock correction, φ' is the latitude of the observer and δ is the declination of the star. a, b, and c* are constants characteristic of the instrument used: a is the azimuth error, b the level error and c* the collimation error. This formula applies to observations made at the upper culmination of the star. For use on observations made at lower culmination, the sign of δ is changed. Bessel's formula and Mayer's formula are equally suitable for computing when, as is almost always the case, the errors in azimuth, leveling and collimation are small. When these errors are large, Bessel's formula should be used.