My perspective on this as a piano technician:This app gets a lot right: concept, usability, and fun.It has great potential to become a high-level ear training tool for piano tuning students, but it's not quite adequate for this use case in its current state. Key improvements that could bring it to this level:- Better audio quality (for some intervals, beating is much harder to hear than it would be in tuning a real piano; in some cases, it's barely discernible even with a bandpass filter set to the frequency of the coincident partial)- Better samples (all unisons need to be absolutely clean, which they aren't at present; alternatively, single strings could be recorded instead of full bi/trichords)- BETTER TUNING. At present, the "correct" tuning is accurate enough to give total beginners an idea of whether they're in the ballpark, which is good. However, there are inconsistencies that are too extreme to be considered acceptable to most piano technicians. For instance, I measured the beat speeds of the M3s in the temperament octave for the app's "correct" tuning:F-A: 7.67 bpsF#-A#: 7.48 bpsG-B: 7.98 bpsAb-C: 9.20 bpsA-C#: 7.89 bpsBb-D: 8.33 bpsB-D#: 10.1 bpsC-E: 9.8 bpsDb-F: 10.4 bpsWhile some imperfection is inevitable, this is hardly an aspirational standard to judge correctness against. If it had an accurate reference tuning, this app could be suitable for serious tuning pedagogy, especially for remote students who don't have the privilege of access to a piano. As it is, it's a generous free offering, but if a serious version were created, it could conceivably sell for $50+ to piano tuning students.Thanks to the developers for creating this fun tool.