Assuming standard atmospheric conditions, the air pressure at sea level is approximately 1013.25 hectopascals (hPa) or 1 atmosphere (atm). The air pressure decreases with altitude following the barometric formula, which states that pressure decreases by about 1 hPa for every 8 meters of ascent.
Using this formula, we can estimate the air pressure at 1200 meters above sea level as follows:
1200 m / 8 m per hPa = 150 hPa
Therefore, the hiker on a mountain ridge 1200 meters above sea level would experience an air pressure of approximately 863.25 hPa (1013.25 hPa - 150 hPa) or about 0.85 atm.