This study has some didactic purposes such as:
a) Increase the knowledge on the harmonics as well as improve the skill for reading and playing them. It is quite common the study of the natural and artificial harmonics (called octave harmonics), usually played with two fingers of the right hand and thus creating a “knot” in the half of the string. However, the secondary artificial harmonics are studied with lesser frequency, that is, those played mainly in the 3rd and 4th parts of the string, and here presented.
b) To develop the movements of the left hand by wide leaps, eased by the used of open strings, but also with a certain technical compromise.
c) To help the student to the difference between the basic rhythm and that of the melody, whose accents do not agree with those natural accents of the beat. This aspect comes first in a plain melody in the high range, and then taken to the lower part, changing the type of difficulties. The melodic ostinato that is presented all the time in this piece intends to evoke the psychological effect of an old traditional train, where the rumor of the machinery is regular and where the passenger can get the sensation of two different realities at
one same time: inside the train time seems to flow normally, once that all the points inside watched by him move all together, whilst looking at the window one can feel the vertigo of the movement. That is the reason of the title as well as the indication Allegretto ossessivo.
d) Practice the alternating notes between the bass notes and the melody, whose lines, quite waved, move in certain moments in a soft, independent and winding way.
e) Practice of repeated fast chords.