  All-sky monitors can measure the fluxes of astrophysical sources by measuring
the changes in observed counts as the source is occulted by the Earth. Such
measurements have typically been carried out by all-sky monitors like
$\textit{CGRO}$-BATSE and $\textit{Fermi}$-GBM. We demonstrate for the first
time the application of this technique to measure fluxes of sources using a
collimated instrument: the Cadmium Zinc Telluride detector on
$\textit{AstroSat}$. Reliable flux measurements are obtained for the Crab
nebula and pulsar, and for Cyg X-1 by carefully selecting the best occultation
data sets. We demonstrate that CZTI can obtain such measurements for hard
sources with intensities $\gtrsim1$Crab.
