  Son of X-Shooter (SOXS) will be a high-efficiency spectrograph with a mean
Resolution-Slit product of $\sim 4500$ over the entire band capable of
simultaneously observing the complete spectral range 350-2000 nm. It consists
of three scientific arms (the UV-VIS Spectrograph, the NIR Spectrograph, and
the Acquisition Camera) connected by the Common Path system to the NTT, and the
Calibration Unit. The Common Path is the backbone of the instrument and the
interface to the NTT Nasmyth focus flange. The instrument project went through
the Final Design Review in 2018 and is currently in Assembly Integration and
test (AIT) Phase. This paper outlines the observing modes of SOXS and the
efficiency of each subsystem and the laboratory test plan to evaluate it.
