Richter tuning is a system of choosing the reeds for a diatonic wind instrument (such as a harmonica or accordion).
This primarily aids in harmony in the key of G, facilitating easy play of the G-C-D (I-IV-V) chord progression, while maintaining a partial G7 (minus the root) higher on the harmonica.
It can occasionally be helpful in some melodies, most notably "The Star-Spangled Banner," which has a low F# and a high F. For example: (Compare this to major seventh tuning, below.)
For example: Paddy Richter tuning (developed by Brendan Power) allows a two octave scale suitable for melody-based music.
It was developed with Irish jigs, reels and hornpipes in mind but is suitable for other melodic music also; it allows pentatonic scales in the stated key and up a fifth; for instance, an instrument in the key of G can play both the G and D major pentatonic scales throughout the length of the instrument).