Thanks for responding, Kevin! Your arguments have some weight and raise precisely the kinds of issues I’m interested in having discussed. I have a Kurzweil Mark-Pro Two electric keyboard, which is clearly a professional level instrument. I just checked its tuning with my gStrings app, and it comes in at A=441.3. I don’t have the owner’s manual handy, but I’d be surprised if it can’t be calibrated, probably by any schmo. Its only previous owner is a Jazz pianist who I’m quite sure didn’t re-calibrate it. Bosendorfers are factory tuned to A=443 (or to order). Some people claim that slightly sharp tuning of certain instruments enhances the sound of a small group when set off against standard tuning of the other instruments. I’m just inquiring here, though, and don’t have a strong opinion one way or the other. The question here is about what works best for the melodica.
I know that standard concert pitch is A=440, but only sort of, since it varies somewhat by country and between different orchestras, and the standard has been debated and has varied over time.