Calibration mode selection.
There are three calibration modes: Manual, Semi-Automatic and Automatic.
Automatic (A). In this mode the firmware determines the need for calibration. The calibration process starts automatically.
Semi-Automatic (SA). The user determines the need for calibration based on the image quality and can action at a convenient time depending on the object being observed.
Manual (M). In the Manual (silent) calibration mode the user determines the need for calibration (as in SA mode) but the lens cover must be closed during calibration.