Abstract: An assembly for reading musical scores and to assist in learning and practicing a polyphonic musical instrument, as well as a process for using this assembly, comprises two flat coacting elements (1 and 2) of which the first (1) which is external and forms a flat sleeve, has on at least one of its side surfaces a series of windows (F.sub.i) each associated with a pictogram (P.sub.i). The second flat element (2), which is internal and in the form of a flat support, can slide with guidance in the flat sleeve forming the first element (1) and bears, distributed over its surface, a plurality of assemblies of groups of data (A, PM), the groups of data of a same assembly being disposed such that they can all appear simultaneously in the windows (F.sub.i). There is a plurality of labels each bearing a predetermined association of a pictogram (P.sub.i) and a group of data (A, PM), the labels being adapted to be fixed at least temporarily on the sheets of musical scores.