The other weekend I did a couple of deep dives off the beach, then later in the day drove over a hill (only around 1,000 ft). A more detailed account is in http://www.scubaboard.com/forums/ask-dr-decompression/503484-driving-hills-after-diving.html If I want to conduct a dive and treat it as an altitude dive for NDL planning purposes, is there any easy way to do it with the Petrel? Gradient factors? My Suunto Vyper has an option for setting the altitude range, but the Petrel is smarter and can figure out the altitude with the pressure sensor. In recreational nitrox mode (which is what I dive), the Petrel is fixed at auto for surface pressure; I have it set to medium conservatism. Reading the full manual, there doesn't seem to be any way to set a starting altitude despite what the pressure sensor reads at the surface, but I could change gradient factors. Is there a recommended method for the Petrel?