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A program I wrote years ago for use in my hp 67 card-reading calculator using RPN logic
See it below (also works with hp 97 and hp 41)

The formula is:
Z= 62900 log10 Po/P

where Z=altitude in feet, P=Pressure at the upper limit in any units, and Po=pressure in same units as above corresponding to zero altitude.

This works well to 12,000' at middle latitudes, and assumes a mean temperature of the air column (isothermal temperature) of 50°f.

Or, to reduce upper station readings to mean sea level,
use the inverse of the log

Po = P [10x (Z / 62900)]

Note: This is the old isothermal calibration standard (Bureau of Standards, Circular No.46). It was used to calibrate altimeters for airplanes between 1917 and 1925--before airplanes could fly much over 12,000'.

But you haven't got an hp 67--hardly anybody does anymore except me!
The old card reader calculator is 25 years old!
Alas, I can't update the calculator,
so I am bringing myself (kicking and screaming) up to date with Excel!

I have used the above formula in an Excel spreadsheet you can download

email me if you have trouble downloading--I will send as email attachment.

for Mac

for Windows

On February 13, 2003 I received this email from Australia:
(I have flipped this 180° for Northern Hemisphere viewing.)


Thanks for the spreadsheet. It works fine. I had to estimate the height of one dam above another dam to see if a windmill could push the water that far uphill.

I borrowed an accurate aneroid barometer and using your spreadsheet & the barometer readings I could calculate that the higher dam is 61 metres above the lower dam.

Shane Lennard
Mount View
New South Wales

You too can use a household barometer to find out the elevation of a height near you. Just record the inches indicated at the starting elevation and then the inches at the upper level; enter them in the above spreadsheet. Household barometers are good for up to about 4000 to 5000 feet, if they are calibrated to 26" or 25" respectively.

If you want to reduce an upper station elevation reading (adjust your new barometer to the elevation of your house) to its sea level equivalent (which is the way all barometer readings are reported), here is an online converter that works with your browser.

It will also calculate the boiling point of water at any atmospheric pressure, so you will know how to adjust the time your 2-minute egg.


f LBL A ENTER STO 1 STO 6 29.97984 STO 5 RCL 1 RTN

f LBL B ENTER 32 - RCL 1 x .0001 x CHS RCL 1 + STO 6 RTN

f LBL C ENTER CHS 211.99 + STO 2

10.1184 STO 3

18.8 STO 4

29.97984 STO 5

RCL 2 RCL 4 ÷ RCL 3 x CHS RCL 5 + STO 6 RTN

f LBL D ENTER STO 5 RTN (always enter after LBL A)

f LBL E RCL 5 RCL 6 ÷ LOG 62900 x RTN

To run:

Button A enters the observed height of the barometer in "Hg.

Button B enters the temperature of the thermometer in °f.


Button C enters the observed boiling point of water in °f.

and, if known,

Button D (optional) modifies the default mean sea level 29.97984 Hg to a known value.

Button E solves for altitude in feet.

My 1976 hp67.

If you are using Apple's OS X, you can get a free virtual hp41CV RPN calculator (a newer classic hp model) from nsim.
Looks and works just like the real deal--fully programable too. And it runs on your computer desktop!
I use this a lot, now.

go The Frémont expeditions and the determination of altitude in 1844

go New reductions of Frémont's 1842 barometric register determine the identity of the 13000' peak climbed in the Wind River Range.

go Pioneering use of the aneroid barometer by Goddard and Day in the Sierra Nevada in 1855.


©1999, 2007
Bob Graham