>Hmmm. Combined with a compass it might make it good enough for simple >inertial guidance inside a house. A compass will show bs inside any house with metal objects in it (such as rebars in the floor and ceiling etc and furniture objects with magnetic metal in them). If you also have dc circuits in the house your north may be *up* or such. Exceptions confirm the rule, beware. Peter -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu