Pythagorean tuning
In a meantone tuning, we have different chromatic and diatonic semitones; the chromatic semitone is the difference between C and C, and the diatonic semitone the difference between C and D. In Pythagorean tuning, the diatonic semitone is often called the Pythagorean limma and the chromatic semitone Pythagorean apotome, but in Pythagorean tuning the apotome is larger, whereas in -comma meantone the limma is larger. Put another way, in Pythagorean tuning we have that C is higher than D, whereas in -comma meantone we have C lower than D.