Schradieck, The school of violin technics, Шрадик, упражнения для развития беглости на скрипке

The most popular exercise by Henry Schradieck we all remember from our childhood.
It promotes the dexterity and develops an accuracy in dropping and lifting fingers.
My own secret is keeping the 4th finger always above the fingerboard, ready to play and slightly stretched, but relaxed at the same time.
To make it more easy to play full speed and make the 4th finger fall on the string effortlessly I practice it with over-extended 4 th finger, I play F instead of E.
Then it feels more natural and less stretchy in a real setup.
Also, I play it on all strings.
How to know you are doing it properly and avoid mistakes? Develop an accuracy, by repeating the whole exercise 8 times, without mistakes, then you know it’s solid. If you made a mistake in a 8th attempt, you have to start over, until you can play it 8 times perfectly.