Most intact human nervous systems know whether they are vertical or tilted, to around 4 degrees of accuracy between the perceived and real displacement.
Compston
Alastair
A
D019336:Cognitive Science / Q000266:history*; D003657:Decision Making / Q000502:physiology; D049669:History, 16th Century; D049670:History, 17th Century; D006801:Humans; D009424:Nervous System Physiological Phenomena; D009462:Neurology / Q000266:history*; D009949:Orientation