That's the hit points tracker of the Eldritch Cannon. Since there isn't a way to track it in the sheet (it's not the same as a Steel Defender companion), the workaround is putting a "number of uses" tracker that is just meant to track hit points of your cannon instead.
Seen here on the Eberron: RftLW bugs & support thread:
I noticed on the sheet that each part of the cannon has 15 uses, but I can't seem to find where it's written down that the cannon has limited uses
Edit: Forgot to mention just incase, this is pertaining to the Artillerist Artificer
That's the hit points tracker of the Eldritch Cannon. Since there isn't a way to track it in the sheet (it's not the same as a Steel Defender companion), the workaround is putting a "number of uses" tracker that is just meant to track hit points of your cannon instead.
Seen here on the Eberron: RftLW bugs & support thread:
Ryan (he/him/his)
Extended Signature
Ahhhh I missed that entirely, thank you!