Hi Gareth, Perhaps you can place a small force (in a known direction) on the sample as you observe the way the fringes shift. This will easily tell you the direction of the height variation (probably a much simpler method than trying to compare the phases of reflected light -- especially because anything you try to do to compare the phases would require a measurement way outside of the coherence length of a reflection!) Just a thought from your friendly neighborhood Japanese translator... Warren _________ Dr. Warren Smith Japanese-English Translation Services Japanese-English Technical Services 1-800-884-5387 ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################