When you select Auto setup for the Oscilloscope, the instrument senses the input signal and automatically chooses many of the instrument settings that best suit the input signal.
If a signal is detected on an analog channel, the Oscilloscope chooses the smallest available vertical range that is larger than the signal range, and an offset to center the waveform within that range. For example, if the signal is a 1.2 Vpk-pk sine wave, the Oscilloscope will choose the 2 V vertical range for that channel. An analog channel is considered to have a signal present if the signal is at least 10% of the smallest vertical range available for that channel and vertical offset.
If a signal is detected on at least one analog channel, the lowest-numbered analog channel with a signal will be used as the Analog edge trigger, and the sample rate and acquisition time will be optimized for that channel.
If no signal is detected on any analog channel, all settings will be configured to default values, and a warning occurs.