Not that the list below has eliminated my talent for edge-planing out of square, and apologies if I’m kicking in already wide open doors.
1. A plane edge square to the side of the blade isn’t a strict requirement, but it helps a little.
2. A thin strip of wood can be used to check that the blade edge is parallel to the width of the sole. I first adjust by visual inspection and tapping with a hammer. When believing the blade is set, I retract it just beneath the mouth; to subsequently advance it until the strip of wood catches when pulled over the edge’s corners. Then I tap until there’s an equal minimal catch. As elaborate as this procedure might seem, it saves time for me, as there’s less need for adjusting out of square planing.
3. Would it be worthwhile to inspect the flatness of the sole, along and across, and particularly around the mouth?
London, UK; Boston, MA