Guido's two lasting inventions both solved the same problem: how to fix the pitch of a chant precisely enough that a singer could learn it from a written page rather than from a teacher's voice alone. The four-line staff, with lines and spaces assigned to specific pitches and colored lines marking the reference notes F and C, let a scribe notate melody with a precision the older neume notation, which showed only the shape of a melodic contour, never fully achieved; a fifth line completed the system within a generation of his death, producing the staff still used today. His so-called Guidonian hand, a method of mapping the notes of the medieval gamut onto the joints and tips of the fingers of the left hand, let a teacher point to a note on the hand and have a class of singers instantly picture its pitch, a mnemonic so effective it remained in use for centuries after his death.
His solmization syllables came from a well known hymn to John the Baptist, Ut queant laxis, whose six phrase-opening lines happened to begin on six successive rising notes of the scale; Guido named each note after the syllable that began the corresponding line, ut, re, mi, fa, sol, la, and taught singers to associate the sound of each syllable permanently with its scale degree. The system spread through Europe within his own century, ut was later softened to do for ease of singing, and a seventh syllable, si or ti, was added afterward to complete the octave, but the underlying method, movable-do solfege, taught in classrooms today descends in an unbroken pedagogical line from the syllables Guido drew out of one Latin hymn nearly a thousand years ago.