This is a warm-up exercise I like to do. It helps me warmup my singles and doubles at the same time while also conditioning accuracy at the same time. Make sure there are no flams between the singles and the doubles!
This is a good exercise to warm up your single strokes and dynamic control in general. It's tricky to accent the last stroke of the group of 6 and requires a fast "whip" of the last stroke which I find really warms up my forearms very well.