The piano keyboard is used as a point of reference when comparing pitch and octave an interval with the same note names but twelve half steps higher or lower between instruments. Counting from the lowest C on the piano, middle C is the fourth C. Thus middle C can be indicated C4. All notes between C4 and C5 are in the fourth octave of the piano. They can be written C4, D4, E4, etc..
Dot shapes are used with the on-screen string instruments to indicate octave. The number of sides of a shape are the same as the octave number. Notes in the fourth octave, C4 to B4, are shown with a square, four sides. Notes in the octave below, C3 – B3, are shown with a triangle, three sides - notes in the octave above with a pentagon, C5-B5.
Count the sides of a dot shape. This number indicates the octave on the piano.