Garmin Striker 4 plus

I spent the weekend working with my toy. Figured out how to move around and change settings. Charted and dropped a couple way points and played with Sonar and Clear Vu settings. I'm getting a line to keft of screen that reads a depth and this value moves around as i move around what is it telling me? See attached pic Reading is showing up as 8.25 on attached pic of screen.

Thanks in advance,

Dave