Reading Sheet Music on the Harmonica  

Since the slide pressed in sharpens the note, it is actually not too difficult to play in all the sharp keys, except that the natural blow/draw rhythm of the scale is different because the draw/draw on A/B comes in a different place.

If the music is in G, for example, you simply look at the signature and know that. for one sharp, all the F's are sharp, in D, F & C are sharp, and so on. C# is a doddle, of course, because all the notes are sharp!

The flat keys are a lot harder because the more flats there are, the more each hole has two consecutive notes on blow (or draw) using the slide.

I believe that the way most people learn to play the harmonica (as a diatonic instrument) is probably the wrong way to learn because that pattern (b d b d b d d b) becomes fixed in the brain before we learn what the notes are. It would really be better to start learning on a chromatic harp with simple pieces in the more difficult keys (how about 'Baa Baa Black Sheep' in Eb for starters?), then one wouldn't learn the 'natural' pattern (of C, for example) and have to unlearn it when it came to other keys! In fact, each piece would have its own breathing pattern which would be associated more with the expression than with the pattern of the scale. (I wonder if I make myself clear!)