Kestrel settings confusion

[ShortShooter1908]

I have an older 3500. If I set the barometric pressure reference altitude to 0, does that mean that when I look at the altitude that the meter shows that is density altitude? Sorry if this is totally wrong or seems confusing but I am getting lost in what is what and the more I read the worse it gets.

Thanks in advance

 

[DocUSMCRetired]

With reference altitude set to 0, what you are seeing is Station Pressure.

Barometric Pressure, is pressure calibrated for altitude.

 

[_Windrider_]

the 3500 doesnt measure DA. Like DOC said, when u set the altitude ref to Zero, all you are getting is station pressure (or absolute pressure as it is sometimes referred to). The altitude reading will then no longer be correct as that requires a barometer setting that has been corrected (what you get from airports or weather services).

 

[ShortShooter1908]

Ok. It's starting to make more sense to me. Is DA more of a short hand for temp, barometric pressure, etc? Is it any more precise that just adding in all the other factors to a calculator?

 

[_Windrider_]

Ok. It's starting to make more sense to me. Is DA more of a short hand for temp, barometric pressure, etc? Is it any more precise that just adding in all the other factors to a calculator?

DA is made of STATION pressure, temp and RH. it is more accurate to use those when creating a solution because a given DA can be derived from many different combinations of those 3 elements. Temp is especially important as speed of sound changes with temp. if you have nothing else though, using DA will get you close. there are easy ways of calculating DA that will get you close. but again, you have a kestrel. use Station pressure and temp from that and just set RH to 50% in your calculator and you will be good to go.

 

[ShortShooter1908]

How does just picking the mid point make things work out?

 

[_Windrider_]

How does just picking the mid point make things work out?

it cuts any error in half. try it. RH makes almost zero difference unless you are shooting extremely long distance, like KO2M distances.

Example:

70 degress
SP 29.92
RH 0%
DA= 717

70 degress
SP29.92
RH 50%
DA = 876

70 degrees
SP 29.92
RH 100%
DA = 1036

Now see what RH actually does to your firing solution? but it barely changes if at all. between 0 and 100% is a DA difference of 319 feet. no way you would notice that. use 50% and the error is only 159 ft.