tuning app recommendation

The gold standard is the Peterson virtual strobe app. However, many less expensive apps will suffice, but they need to have the following:

1. The ability to set the reference pitch to something other than A440. Most harmonicas need to be tuned to a higher pitch standard, such as A442 or A443. Many out of the box harps are tuned much higher. If you need to put a few notes in the harp in tune with the rest, then you need to figure out what the harp is tuned to overall. Or you may wish to change the reference pitch if it's too low or too high for your uses.
2. The ability to see exactly how many cents a note is above or below the target pitch. Most harmonicas are not tuned to equal temperament, and to get the tuning right you need to know how many cents flat or sharp the note should be, how close the note is already, and how much you've changed it as you tune.
3. The ability to store different temperaments, with built-in variants from equal temperament (such as 7-limit Just for classic blues diatonic tuning, or 19-limit just for a more more modern sound), might be nice. Pesonally I prefer to just work with the deviations from equal temperament, and then rely on my ear for final testing. Also, if you're tuning to one of the compromise tunings, the onyl way to do his is with variations in specified numbers of cents from qual temperament.

Available apps will depend on what you're going to use them on - iPhone or Android, Windows/Linux/Mac - each has a different set of apps available.

Harmonicas use a few different temperaments, depepnding on the model.

The old tuning you hear on blues records up through the 1960s is 7-limit Just. This sounds great for chords but Draw 5 sounds really flat as a melody note.

Here's one of Pat Missin's tuning pages that gives some information:

http://www.patmissin.com/tunings/tun6.html

Also, check out another thread from kinya's forum:

https://www.bluesharmonica.com/equal_tempered_and_just_intonation_tunings

Here's a review of some low-cost tuners for iPhone:

https://appadvice.com/appguides/show/tuners-for-the-iphone

And here's the gold standard for tuners, Peterson virtual strobe tuners:

https://www.petersontuners.com/products/istrobosoft/