All Kestrel meters with altitude function measure air pressure in order to calculate barometric pressure and altitude. Changes in either air pressure or altitude will affect these readings, so it is important to make adjustments as necessary if you bring your Kestrel to a higher or lower altitude.

You will need either:

Your current altitude (www.whatsmyelevation.com)

OR (you don't need both)

Your barometric pressure (Google it, or call local small airport)

Let's assume you know your altitude.

Scroll through the Kestrel meter to the Baro screen. It is here where you will adjust your 'reference altitude'.

Now, read the barometric pressure it gives you. That will be your reference pressure. Go to the Alt screen, and adjust the Reference Baro (Ref Baro) doing it the same way as above.

As you are doing that, you will notice that the altitude reading will change as your reference pressure changes. When you are finished, press the center button to exit the adjustment mode.

To adjust the barometric pressure first, first you will need to obtain your altitude from a topographical map, landmark or the Internet. Once you have that number, scroll to the "Baro" screen which is your urrent Barometric Pressure on your Kestrel. Once there, press the center button to enter the adjustment mode.

Again, use the left and right arrows to adjust the reference altitude. Again, you will notice that the Barometric Pressure will change with changes in the reference altitude. When you are done, press the center button to exit the adjustment mode.

For novices', a truly step-by-step instruction of how to do this from customer feedback:

1. Cycle to bAro screen
2. Push left and right buttons together to see 'REF' Alt
3. Use left or right buttons to adjust to current altitude
4. Push left and right buttons together to exit 'REF' mode
5. Note (write down) the bAro pressure
6. Push right button to see 'Alt' screen
7. Push left and right buttons together to see 'REF' bAro pressure
8. Use the left or right buttons to adjust the 'REF' bAro pressure to match that noted above
9. Push the left and right buttons together to exit 'REF' mode
10. Done

Why does it fluctuate and how often to I adjust it?

There are certainly advantages with GPS... pros, and cons. With any barometric altimeter, you're going to have the issue of pressure changes affecting your altitude.

Here's how it works and you can decide if a baro/alt is the right way for you. If your goal is getting proper barometric pressure consistently, while at the same altitude, this can be done. You set your reference altitude (on the baro screen) to your current altitude.
If you are not changing altitude, your barometric pressure reading will remain accurate and you can watch changes and trends with the weather. The problem is, if you go hiking and change altitude dramatically, the barometric pressure will then be off until you readjust your reference altitude.

There is no real way to lock in the altitude to be accurate all the time, as it is solely based off of the meter’s pressure sensor. They are not GPS.

That being said, it can be a useful tool. If you are going for a hike, you should really set your reference barometric pressure before you go, and then along the way you can track your current altitude. If there is little pressure change, it will remain very accurate, and typically for a day it should not get off too much. For longer journeys, however, you will have to readjust your reference barometric pressure as you go since the atmospheric pressure is bound to change. One tip is that if you run into an elevation marker on your journey, use that elevation as your reference altitude on the Baro screen and then you can use that number for the reference baro on the altitude screen. This is especially helpful when in remote locations without wireless access and can’t access current weather reports.

That's how it works with any Baro / Alt meter. I should note, that Kestrel are very sensitive intentionally for accuracy, so seeing some bounce is totally normal. That too has pros and cons, but for our accuracy in barometric pressure, it was important.

Station Pressure vs. Barometric Pressure

If you set the reference altitude to zero feet/meters, then the Kestrel will be reading Station Pressure. Station Pressure is the pressure felt without adjusting to sea level.

If you set the reference altitude to your current altitude, then the Kestrel will be reading Barometric Pressure. Barometric pressure is pressure adjusted to sea level. This can also be called Mean Sea Level Pressure.