Practising on the open string helps us to focus on one technical issue at a time. Notice how the elbow movement keeps the bow close to the string.
To begin exaggerate the range of the movement, ‘levering’ the elbow quite high on the down bow and dipping it quite low on the up bow. However when we come to play the passage in tempo, the movements are refined and less noticeable.
Notice the differences in bow division when we phrase off at the end of a phrase unit, for instance in Bar 4.