Brode's group investigated the fusing systems, testing radar altimeters, proximity fuses and barometric altimeter fuses. Some skydivers wear a visual altimeter, and some use audible altimeters fitted to their helmets. Such features include GPS, compass, barometers and altimeters. Typical applications include miniaturized weather stations, electronic barometers and altimeters. Measurement instruments like pressure gauges, altimeters and barometers include linkage-type function generators as linearization means. In 1717, Fahrenheit settled in The Hague as a glassblower, making barometers, altimeters, and thermometers. The instruments included altimeters, thermometers, compass, clock, and a Telefunken P63N radio goniometer. Hikers and mountaineers use hand-held or wrist-mounted barometric altimeters, as do skydivers. FM-CW radars are very widely used as radio altimeters in aircraft. From the early colidar systems all laser rangefinders, laser altimeters and lidar units are derived. The cockpits included new MFDs, HUDs, HOTAS controls, radar altimeters and RWRs. Radar altimeters generally only give readings up to above ground level (AGL). Reversal errors primarily affect altimeters and vertical speed indicators. Tools such as GPS and altimeters are forbidden. Derivations like altimeters for parachutists will follow and are produced well into the Internet age.