# Observing time calculator

Please go to this page for the new observing time calculator: http://www.apex-telescope.org/heterodyne/calculator/**PWV [mm]**[0.05,0.1....3] τ

_{zenith}

**RMS calculator**

**Integration time calculator**

By entering
the atmospheric temperature (some 10 degrees below the ground temperature at Chajnantor),
the (average) elevation of the source, the receiver temperature, an on-source integration time,
and the spectral resolution, the σ (in K) can be estimated. See the
observing time calculation page for details. The APEX-2a receiver
temperature is about 70 K for the entire tuning range.

By entering the
atmospheric temperature (some 10 degrees below the ground temperature at Chajnantor), the
(average) elevation of the source, the receiver temperature, required σ (in K), and
the spectral resolution, the on-source integration time can be estimated. Also the total
time is calculated assuming t

_{off}=t_{on}and a system observing efficiency of 0.625, i.e. t_{total}=(t_{on}+ t_{off})/0.625. The system efficiency takes into account time for telescope movements and calibrations.-->