12 ET, I think from our discussions here, Weiyan. I have an M-37C, though it is not so seriously out of tune and I have not yet tuned it. I also have the Suzuki A-34C and the Suzuki M-32C. These both came tuned sharp at about A4=442. I ended up tuning them down to A=441 and A=440, respectively. I play my melodicas a lot with Band-In-A-Box, and they sound better at those flatter tunings. There’s an investment of time involved, but it’s worth figuring out where you want to be and tuning to there. I started out tuning to A=443 but was persuaded to get closer to 440, and I’m happy with the results.