The display MAY be showing the TARE weight of the tank which would probably be near the 13Lb you are reading. There may be a reset for this to zero it. I have a different unit so I can only point out possibilities.
I would carefully read the proceedure to make sure all steps you are using are correct... If a connection is not quite right that might be blocking the recovery.
Answers & Comments
The display MAY be showing the TARE weight of the tank which would probably be near the 13Lb you are reading. There may be a reset for this to zero it. I have a different unit so I can only point out possibilities.
I would carefully read the proceedure to make sure all steps you are using are correct... If a connection is not quite right that might be blocking the recovery.
Pls don't do any thing. You just need to re-calibrate the scale thats all