I get usefully accurate altitudes with my now discontinued Foretrex 101. My driveway slab is precisely 200 feet above sea oevel. The other day my Foretrex gave an altitude of 204 feet. I thought, that's pretty close, and then realized I was holding it at waist level...

The 101 does not alwaysgive an accurate reading, especially when first turning it on, but it will settle down and provide good info.