A 4-2-1 duplet grid with a triplet variant of the Five Stroke Roll featured as the moving pattern.
In other words, there are three consecutive embellishments being shifted across four partials: A single accent followed by two double strokes.
This results in an overlapping effect during the third and fourth variations of the sequence. The fourth variation is cut off at the end to compensate for the beginning of next sequence.
This approach is used with the grid featuring the Lesson 25 rudiment as well.