The Exposure Time Calculator (ETC) is a tool to predict the performances of the spectrometer for different parameters and environmental conditions.

The ETC computes:

• the limiting magnitude (in AB units) achievable at a given wavelength, in a given exposure time and at a given signal to noise ratio and the limiting surface brightness (in AB mag/arcsec²) achievable at a given wavelength, in a given exposure time and at a given signal to noise ratio;
• the signal to noise ratio achievable for a compact source at a given wavelength, in a given exposure time and at a given AB magnitude;
• the signal to noise ratio achievable for an extended source at a given wavelength, in a given exposure time and at a given surface brightness.

The ETC takes into accounts a number of instrumental end environmental parameters that can be modified to evaluate their effect on the overall performances of the spectrograph.

ETC for limiting magnitude and limiting surface brightness

ETC for S/N ratio for compact source

ETC for S/N ratio for extended source