I wish I remembered what TV show I saw this on at 2am. They showed a video from the 50s of a self propelled walk behind mower of about 21". They walked behind the mower one complete circle and then let it mow by itself until done. The video did not show the mower up very close but it had some arm in front of the left front caster wheel that pivoted. This arm was just above the height of the cut grass and would get pushed sideways when it touched the taller uncut grass. As this mower moved foreward it basically hunted left/right constantly but still did its job. I find looking around the www.USPTO.gov website as confusing as trying to understand the federal tax code. I would love to see better the mechanicals of this mower. Anyone else see it or understand how to find that patent? I hope this mower still exists as my guess is none were manufactured.