Exbal, Loadbase, different results

[Trent]

Just got a new brunton adc weather station and was playing around with it to see how to set the barometric pressure on my palm in exbal. I set the altitude to 0 and unclicked the calculate std pressure and entered the pressure reading off of the brunton and recorded what it said for comeup at 500, 700, 900 and 1000. On my computer i have loadbase 2.0 which i had previously got before i got the hand me down palm pilot and exbal. In loadbase i typed in the altitude and current barometric pressure given from the local air strip which is only about half mile away at roughly exact same elevation. All other info entered was the same except for drag coefficient which i left at .5 on loadbase since i was not sure what to put and never seen this on exbal. The results for 500 and 600 were within about inch in drop and the same moa for the load i entered. At 900 they varied 3 inches and at 1000 just a little over 6 inches.
After seeing these differences i then changed the loadbase data to station pressure and entered the reading off the brunton. When i did this it atomatically took the altitude figure out. I then compared these results with exbal and the were still off. These readings were almost the same as the previous loadbase figures.
I am really new to this and trying to get set up on a limited budget and was just playing around with the numbers. When it warms up planning on making drop chart off actually shooting and getting actual bc. I am wondering if i am doing something wrong with these programs or do they just vary that much. I checked my input numbers twice on each to make sure i entered the same values.
Any help or info much appreciated. Thanks!

 

[Michael Eichele]

Sounds like you are doing it about right. Make sure altitude is set to 0' if using station pressure. Also some programs use 29.92 standard pressure and others use 29.53. This could cause the discrepencies between programs. It will however depend on how well the program was written. I have seen some programs that used 29.53 and other that used 29.92 and they matched with in 10ths of an inch. Also some programs use slightly different mathematical formulas causing minor differences. Also it sounds like you were using your Brunton for one program and an airport for another? If one guage is slightly off from another it can cause small discrepancies. A 0.40 difference can cause the descrepancies youre seeing.

The important part is that you gather real world data and use this to figure your ballistics with your programs. Something maybe slightly different in each program such as your BC.

 

[Trent]

The first time i did use two diffent readings. Used brunton reading on exbal and airport on loadbase. The second time i used the brunton reading for both. When i did this the airport results and brunton results were right on with each other in loadbase, but differed from the brunton results in exbal by 6 inches at 1000.

 

[Trent]

Thanks for the reply.