Keep inside the painted line while digging your trench. In this case the plans call for a trench that is 400mm wide. Our shovelhead is 200mm, so we use that as a guide to measure the width of our trench as we go. Dig until your trench is as deep as your plans require. Then use the blade of your shovel to neaten up the trench walls. Once the trench is finished, get the building surveyor back to approve it and you are ready to pour your concrete footings.