If that is the goal, it'd be better to just play every reed on the axe. Even a straight chromatic scale won't hit every reed. I do the following each time I'm going to play a particular harmonica, it's kind of fun:
- Start at the bottom hole, button out and blow that note, then move to hole 2 and blow with the button _in_, next hole, blow with button out, repeat this pattern all the way up to the last hole
- Next, start at the top hole, blow with button out, same pattern as above but going down (button out, button in, button out, etc...)
- Now repeat both of the above steps, but with all draw instead of blow
Following that you've hit every reed on the axe. After you get used to the pattern, it's very quick to test all the reeds and it almost sounds musical :-).
Caveat: this assumes your chromatic has an even number of holes.
For bonus points try doing the above without pausing your breath at all between notes (so, a continuous stream of air) while still hitting each note cleanly. This will help to improve your slide and positioning technique while testing the reeds.
Of course there _are_ many good reasons to practice scales, and there are so many kinds of scales to practice!
- Slim