Total ozone amounts can also be deduced from observations on the clear or cloudy zenith
sky. The zenith sky data can be reduced by means of empirically constructed charts or statistically
developed equations which relate instrument N, μ, and X values. Such charts or equations are
derived using quasi-simultaneously obtained data from direct sun observations and observations
on the clear or cloudy zenith. More detailed methods using the statistics of the quasi-simultaneous
data have been developed. Detailed information concerning methods and data reduction is
presented in Sections 6.2.4 and 7.3 of this manual.