This magical "9:10" visually appears as a square.  You could verify this by drawing a rectangle on squared paper.  It is simple to draw a rectangle of 9 squares of height and 10 length, isn't it?  It appears almost square, but it's certainly a rectangle!  

Now place the PON's contour into this rectangle in such a way that certain anatomical points touch the walls of the rectangle.  Front vertical wall crosses the shoulder joint, back vertical wall touches the point of the buttocks (ischial tuberosity).  Be sure to exclude the coat.  

Horizontal lines are: upper at the level of withers and lower at floor level.  A well structured dog will fit into this frame easily.  For example: a PON of 50 cm height should be 55 cm long, while a dog measuring 48 cm at withers should be 53.3 cm long.  

The above examples illustrate correct proportions of height to length and the depicted dog appears visually compact and almost square (Fig.1)

A dog with correct angulations of fore and hindquarters but incorrect proportions does not fit into the previously described frame.  An elongated silhouette is definitely a rectangle and exceeds the vertical borders of the frame.  

Proportions are not 9:10 as the standard is incorrect. (Fig. 2)

The fact remains that although a particular dog may fit the frame, it does not prove that the dog is correctly structured.  A PON with an excessively long back and steeply angled hindquarters, in spite of the correct proportions (height/length ratio) will have improper movement.  

A dog with this problem has a much shorter stride and weaker forward drive. (Fig. 3)

A similar situation exists when a dog has the correct proportions and fits the frame in spite of the fact that the loins are too long and the front angulation is too steep. (Fig. 4)

The space that should be occupied by a correctly angulated front is filled by an excessively long body.  A dog structured in this manner keeps the head too high and has a much shorter front stride. (Fig. 5)

Front legs tend to swing excessively upward.  Often this type of dog handled "à la terrier" achieves great awards, because it is "different".  A dog with his head held up high appears more attractive and "professionally" handled.  This is not, however, a typical PON movement or silhouette.

A PON with excellent proportions and good leg angulation (not exaggerated though) possesses a harmonious and compact silhouette, a straight back and well pronounced withers.  The stride is long and ambling.  The head is carried naturally in an almost horizontal position slightly above the line of the back.  Is is truly a great pleasure to watch this movement. (Fig. 6)