A bit late, but figured it’s worth posting. Any ‘off’ readings, always come back to poor connection/contact. Even with the test leads. Cleaned, and made sure there was a good bite… and all was ok. 99% isopropyl alcohol… cleaned the leads, and posts.
If you have a multi meter, try using those leads (if they’ll fit). Once cleaned, my unit calibrates to spec every time… and it’s done every time it gets used.
Plz let us know how you make out.