While once a very effective and useful app, the needle/note readout is constantly in motion across a huge range of notes, making tuning virtually impossible. I thought maybe ambient sound was affecting it, but other tuning apps are not experiencing similar issues. This surfaced after a previous iOS update ( around 8) and continues to date (9.3.5). Not currently recommended. If the issue was resolved, I would highly recommend.
Schmiggly Reeves about Cleartune, v2.1.3