>Thats not too bad, the average aircraft altimeter is +/- 75 feet. Even >after we ran them through the shop they were never dead on accurate. Yeah, if you get a GPS receiver where you can get at the raw data, and leave the aerial sitting at a stable point for an hour or so, and collect data, it is quite revealing how the "position" wanders. And this is with SA turned off :) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.