  ASTRI-Horn is the Cherenkov telescope developed by INAF and operating in
Italy on the slopes of Etna volcano. Characterized by a dual-mirror optical
system and a focal plane covered by silicon photomultiplier sensors, ASTRI-Horn
is a prototype of the telescopes proposed to form one of the pathfinder
sub-arrays of the Cherenkov Telescope Array Observatory in Chile. The
electronics of the ASTRI-Horn telescope, optimized to detect nanosecond burst
of light, is not able to directly measure any continuous or slowly varying flux
illuminating its camera. To measure the intensity of the night sky background
(NSB) in the field of view of the telescope, the firmware of the ASTRI-Horn
camera continuously performs the statistical analysis of its detector signals
and periodically provides in output the "variance" of each pixel, which is
linearly dependent on the rate of detected photons; in this way, an indirect,
but accurate measurement of the NSB flux is obtained without interference with
the normal telescope operation. In this contribution we provide an overview of
several calibration and monitoring tasks that can be performed in a
straightforward way by the analysis of the "variance" data such as the camera
astrometry, the actual telescope orientation and the monitoring of its optical
point spread function.
