A0 is the analog pin that all those 48 pins on the muxshield are being sent to. So, the mux shield works by addressing a channel (one of the 48 inputs.) This connects that input to A0.
A0 is the analog pin that all those 48 pins on the muxshield are being sent to. So, the mux shield works by addressing a channel (one of the 48 inputs.) This connects that input to A0.