There is at least one mechanical design which (claims to?) solve this problem, Wavetrac. Don't want to embarrass myself trying to explain it, so click "how it

There is at least one mechanical design which (claims to?) solve this problem, Wavetrac. Don't want to embarrass myself trying to explain it, so click "how it works" on this page: http://www.wavetrac.net/technical.htm http://www.wavetrac.net/technical.htm