In the old days ... when we carried barometric altimeters (I had a pricey Thommen - actually, I still have it somewhere in the basement) when hiking and climbing you would always reset when you knew precisely where you were - trail intersection, lake, pass or summit. If on an overnight trip, you would check the "altitude' when arriving and then check it the next morning, resetting to match that prior reading. I miss my Avocet 50!!!!