A device and method for monitoring variations in the distance between an object and a datum, comprising: a light source, an astigmatic system for projecting an astigmatic image of the light source onto the object, the astigmatic system including the datum; and image shape detector means for detecting...http://www.google.es/patents/US6678060?utm_source=gb-gplus-sharePatente US6678060 - Monitoring distance variations
