A Kestrel 4000 is a weather meter. One of the best, if not the best weather meters on the market.
It tells date and time of storage. Barometric Pressure, Altitude, Density Altitude, Temperature, Humidity, Wind Speed, Wind Chill, Dew Point, Wet Bulb, and Heat Index.
It stores this info into charts that you use for many things.
Its of great interest while in the field for long range shooting but the usefulness of this information is endless. From camping, to hiking, rock climbing, aviation, fishing and of course all shooting sports.
Let me know if your interested.