Re: used kestrel 2500 or 3500??
3500, only because i got a really good deal on it...yes, it is uncorrected. you can correct for either altitude or pressure.
meaning you can input your exact altitude and it will read the pressure trends based on the weather.
you can input your reference pressure for where you start at and then as you climb you will get your accurate altitudes.
leave both reference settings at 0 and do neither and it will give you station pressure or uncorrected pressure at your location.
at least that's what I can get from the manual after reading it a few times.