Counterexample: a dozen (+1, 0) tiles followed by a dozen (-1, 0) tiles. Vector sum is fine, total angle is fine, but at each end you have an impossible 180 deg

Counterexample: a dozen (+1, 0) tiles followed by a dozen (-1, 0) tiles. Vector sum is fine, total angle is fine, but at each end you have an impossible 180 deg connection. I don’t think you can get away from local measures of tension with a global look.