Garmin Instinct Barometric Altimeter

Hi...

 

I have testing the Garmin Instinct for swimming at warm water . Have find out that the barometer figure is not change at all ,but for altimeter figure is drooping until to the negative .

 

For info I have set the barometer setting in ‘watch mode’. I also already read through some info at Understanding Barometric Altimeter Watch Modes on Outdoor Watches .

 

It is accuracy enough the barometer and altimetry for this watch to measure? I worried that when go for outdoor activity (ex: boat , forest adventure) , the sensor setting of ‘watch mode’ will only taking effect at altimeter only and not change at barometer ? It is possible that barometer and altimetry will both measure as well time to time ?And not only at one altimeter  .

 

Thanks in advance.