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Interpolation Question

Asked by: 1320 views Private Pilot, Student Pilot

I am confused with how to properly interpolate between the two given pressure conversion factors and whether the pressure conversion factor for 29.96 would be positive or negative?

If the outside pressure is 29.96 in. Hg. and the pressure conversion factor for 29.90 is -32 feet and the pressure conversion factor for 30.00 is +68 what is the pressure conversion factor for 29.96?

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1 Answers



  1. John Scarry on Oct 18, 2021

    Standard pressure is 29.92. Pressure below that has a negative conversion factor. Pressure above that has a positive conversion factor. So right off the bat we know that the conversion factor for 29.96 is going to be positive.

    To interpolate you just use the same rule you would use for any other interpolation. The difference between the two given pressures is .10 in and 29.96 is 60% of the way between the two.

    The conversion factors can be a little confusing but think of it this way, to get from 29.90 to 29.92 requires a 32′ conversion factor.To get from 29.92 to 30.00 requires a conversion factor of 68 so the total is 100.

    60% of 100 is 60 so add that to the -32 and you get a conversion factor of 28. Or do it the other way around and go from the 30.00 level. Subtract 40% of 100 from 68 and you get 28.

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