Ultimately Johnston came to develop his own special teaching hand which he called a foundational hand. He felt it was the vehicle through which he could teach the foundations of calligraphy. He made a number of teaching sheets which illustrated the lessons he wished to convey, several are held in the CSC collection.
This teaching hand still forms the basis for much calligraphy teaching today; it conveys the lessons Johnston felt were crucial - consistent weight, pen angle and form - and because in this case the underlying form being aimed at is circular it gives a particularly strong mental image of a shape to aim at. A circle is an unambiguous form, it either is a circle or it is not. If you begin your lettering studies using an oval as the basic form this gives a much less precise shape to aim for, the shape of a circle thus has an educational value.
Johnston's application of his analysis of calligraphic form can be seen in the successive teaching sheets he made for his classes and in the sheets made by his pupils. Very similar analysis can be seen in any calligraphy book published in the USA or UK today.