Microtones are notes that fall in between a black key and a white key. The note in between C and D is C#, and the note between C and C# is Ct (C 1 quarter tone sharp) These microtones essentially go up or down 1 quarter step, which is half of a half step. Consider a sharp, it makes the note go up by one half step. A flat makes it go down one half step. A one-quarter-tone-sharp makes it go up by 1 quarter step, and a three-quarter-tone-sharp makes it go up by 3 quarter steps. Same thing for quarter-tone flats. By adding .5 at the end of a number using the note blocks provided in scratch, you can make quarter tones. You can't play these notes on the keyboard that pops up, but you can play them by clicking on the block.