Question about tuning a harmonica "correctly'
Don't stress out about all the numbers! I just got asked a question about how to tune a harmonica "correctly" using 442Hz and offsets. Here's my answer:
Don't worry so much about tuning "correctly" when trying to wrap your head around all the numbers (443 Hz, 442, 439, etc...) Know that harps that are tuned to Equal Temperament at the factory are usually tuned with an accuracy of + or - 6 cents! That is a very large margin of error. We only need more accuracy when we want the chords to sound in harmony (as in "harmonica").
Let your ears decide. Play single notes and play chords. If something sounds not right to your ears, you have the means to fix it. Play various pairs of notes and figure out which note(s) is/are the culprit. Then use "the numbers" and your ears to fix them. The "numbers" (offsets) are a tool to *help* you make the harp sound right. But it doesn't work the other way around. There is no expectation that you need to validate the tuning of a harmonica by looking at a number on a tuner. Single notes on harmonica are so unstable that using that method is very inaccurate. Just play it and if it sounds good, success!
Tuning by numbers as I describe in the tuning sheet you got is a quick way to do things. You will not achieve perfect accuracy using numbers alone. You need to use dynamic breath force while playing two notes at the same time and let your ears guide you. The methodology to do that is on my website and the link is in the documents that came with the tools. There is also a breath chart on the sheet.
The numbers do serve as a landmark to get you close. It's generally a little easier to set the tuner calibration to 339 and tune to make the needle aim for the zero mark instead of leaving the calibration at 442 and tuning to -12 cents. That's why I recommend changing to 339 Hz when tuning major thirds. Fifths are only about two cents sharp so somewhere in between 442 and 443. But we will hit the 2 draw a little harder so it's maybe best to tune it a little sharp, hence tuning the tonic of the draw plate to 443 instead of 442.5. Also, since those reeds are on the low end of the harp, we naturally tune them a little sharp anyway so the 3 blow may indeed be tuned to 443 anyway once you are done.
I hope that helps! Let me know how it goes!