On Thu, 9 Jan 2003 jmartin@COMP.UFSCAR.BR wrote:

> Scott, i4m trying to do an altimeter based on pressure altitude.
>
> So, the eq is:
>
> H = 44330,769[1 - (P/P1)^0,190255]
> Where H is the altitude, P is the air pressure at altitude H at
> a given and variable sea level pressure P1.

That doesn't answer the question. Again, what are dynamic ranges of P and
P1? Do these come from an 8-bit A/D converter or what? You originally
asked for 32-bit precision, but I doubt you need it.

It'd probably make sense in a PIC to re-write this equation like:

H = A * ( 1 + P^B * (1/P1)^B)

Use a lookup table to compute f(x) = x^B and then perform the simple
arithmetic computation that follows. Of course, you'll need to scale the
1/P1 in a range suitable for the table. But I can't tell what the scale
factors should be without first knowing the dynamic range of your
variables.

Scott

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