I was always taught that a sketchbook was a place where you needn't finish a picture. When you have achieved what you set out to do that is when you stop. I find this a useful practice, it allows me to make mistakes, to push, to warm up. I sketch every day, sometimes working from memory and sometimes on location.
These sketches are about the Thames path between Marlow and Henley.
Riverbank
Long walk, bright light on the Thames
Thames movement
Thames movement
Dark Thames
Winter morning
Cold afternoon