EZON H009 Multi-Functional Hiking Watch with Altitude Barometer Men's Climbing Digital Watch This hiking watch can calculate the altitude base on the sea level pressure; it can measure and calculate the current altitude, relative altitude and absolute altitude. By measuring the local air pressure with sensor, and based on the sea level pressure and ISA (International Standard Atmospheric Pressure Conversion), this watch can calculate the current altitude. But the sea level pressure will be difference due to the different geographical regions, seasons, climate and time period. So you must setup the current sea level or current altitude to calibrate the altimeter before measuring the altitude. Setting Sea Level Pressure: You can find sea level pressure in Local Observatory.<br> This hiking watch can measure the local air pressure by air pressure sensor, and based on sea level pressure and ISA(International Standard Atmospheric Pressure Conversion) This hiking do the weather forecast by barometric pressure trends. In order to improve the accuracy of weather forecast, please set in the current weather status. There is a hundredths timer with 1% second stopwatch in our watch. The maximum time period of the stopwatch is 99 minutes 59 seconds and 99. It can further divide into single stopwatch and split according to the different methods of usage. The maximum of stopwatch measurement is 99 hours 59 minutes and 59 seconds. It has two ways to measure: single stopwatch and split stopwatch.