The English concertina, invented by the physicist Charles Wheatstone, enjoyed a modest popularity as a parlor and concert instrument in Victorian Britain. Wheatstone designed several button layouts for the concertina consisting of pitch lattices of interlaced fifths and thirds, which he described in patents of 1829 and 1844. Like the later tonal spaces of the German dualist theorists, the concertina's button layouts were inspired by the work of eighteenth-century mathematician Leonhard Euler, who used a lattice to show relationships among pitches in just intonation. Wheatstone originally tuned the concertina according to Euler's diatonic-chromatic genus before switching to meantone and ultimately equal temperament for his commercial instruments. Among members of the Royal Society, the concertina became an instrument for research on acoustics and temperament. Alexander Ellis, translator of Hermann von Helmholtz's On the Sensations of Tone, used the concertina as a demonstration tool in public lectures intended to popularize Helmholtz's acoustic theories. The English concertina's history reveals the peculiar fissures and overlaps between scientific and popular cultures, speculative harmonics and empirical acoustics, and music theory and musical practice in the mid-nineteenth century."
Now here is an extract taken from Lee Oskars NOTES ON TUNING A HARMONICA.
"If you tune each note exactly to pitch according to your tuner, the result will be in so-called equal temperament. Equal temperament is common on many models of harps, such as the Lee Oskar Major Diatonic and the Hohner Golden Melody. This tuning is optimized for playing single notes and melodies, but the chords will sound a bit out. To make certain chords sound better, many harps are tuned to a justified (or just) intonation. Just intonation involves modifying the pitch of certain notes to make some chords sound better--but melody notes may sound flat or off key. Various compromised intonations that aren't quite just intonation and aren't equal temperament have been devised to try to work as well as possible for both melody notes and chords."
Jack, your statement was plain wrong, the lee oskar diatonic is tuned to equal temperament.
in my opinion the lee oskar MAJOR DIATONIC is the Diatonic harmonica that sounds best played with an English concertina.