I've seen a really bad stuttering invicta on someone's wrist once, and my Miyota PO had a stutter especially towards gravity. Just investigating the stutter, came across this page that was interesting.
http://members.iinet.net.au/~fotoplot/invicta/invicta.html
http://members.iinet.net.au/~fotoplot/invicta/invicta.html