Open the tool. On iPhone, it's called "Level" and found in the Measure app (or in the Compass app if you're running iOS 12 or ...
ARC stands for Audio Return Channel. It's a standard tethered to HDMI, the same cable type you use to direct video to your TV ...
HDMI ARC, HDMI eARC, there are multiple HDMI ports on every smart TV these days, so it's understandable if it's hard to keep ...