Graduale_Simplex
Graduale simplex ("Simple Gradual") is a gradual in Latin and in Gregorian chant, published by the Vatican in 1967 following the Second Vatican Council, so that the use of Gregorian chant can adapt to smaller parishes and churches or to those who lack experienced choirs.
Its full title is Graduale simplex in usum minorum ecclesiarum (simple gradual for the use of small churches).