An altimeter watch tells you how high you are by measuring atmospheric pressure, since air pressure drops predictably as you climb. The category was born in 1962 with the Favre-Leuba Bivouac, the first mechanical wristwatch to carry both an altimeter and an aneroid barometer. It used tiny metal capsules that expand and contract with pressure, driving a hand around a bezel marked to 3,000 metres of elevation with an inner scale in mmHg. Paul-Emile Victor wore one in Antarctica, and Junko Tabei had a Bivouac on her wrist during her 1975 Everest summit. The hand-wound FL251 calibre inside made it a genuine instrument, not a novelty.
Today the field splits three ways. On the mechanical side, Favre-Leuba revived the idea with the Raider Bivouac 9000, shown at Baselworld 2017 and able to mechanically measure altitude to 9,000 metres. For analogue-digital instruments, the Breitling Aerospace Evo runs a COSC-certified SuperQuartz Calibre 79 in a 43mm titanium case, with crown-operated chronograph, countdown timer, second time zone, alarm and minute repeater; retail sits around £3,600 to £3,800 for 2024, with used examples roughly £1,900 to £3,900. The real volume lives in digital ABC watches: the Casio Pro Trek PRW-6900 reads altitude from minus 700 to 10,000 metres via its Triple Sensor, logs 30 readings, and runs solar with Multi-Band 6 atomic timekeeping. Its list price is around £420 but it has dipped to £250 to £310 in 2025-2026. The cheaper PRG-340 runs about £200, and the Suunto Core sits at £160 to £185 with a 12 to 18 month battery from a single CR2032.
Buying comes down to how you will use it. Barometric altimeters are accurate to roughly 10 to 50 feet once calibrated, but they drift with weather: a 4 hPa pressure drop ahead of a storm reads as about 120 feet of phantom climb even if you never move. That means you must recalibrate at known elevations, a trail sign or a summit marker, throughout the day. GPS-derived altitude is less precise, around 400 feet, but it does not drift, which is why watches like the Garmin Instinct 2 blend both. For pure hiking and mountaineering, a long-battery ABC watch like the Suunto Core or a solar Pro Trek is the sensible pick. If you want aviation heritage and daily polish in one watch, the Breitling Aerospace is the one to chase.
From a collector's seat, mechanical altimeters are their own quiet obsession. Vintage Favre-Leuba Bivouac references such as the 53203 climb to serious money at auction, and because the aneroid capsule is delicate and hard to service, condition is everything. If you simply want reliable elevation data on a real mountain, a solar digital Pro Trek remains the safest entry, both on price and on toughness.