(12C) Body Surface Area

[C.Ret]

(07-28-2021 04:34 AM)Gamo Wrote:  The calculation is from the formula of DuBois D, DuBois EF. 1916
A formula to estimate the approximate surface area if height and weight be known.

Formula: LogA = (0.425 LogW) + (0.725 LogH) - 2.144

Effectively, the original formula from Delafield DuBois et Eugene F. DuBois publication is \( A = 0.007184 \times H^{0.725} \times W^{0.425} \).

If we are looking for the decimal logarithm of \(A \) we get the exact formula that Gamo indicates ; \( \log(A) = 0.425\times\log(W)+0.725\times\log(H)-2.14363 \) where \( -2.14363 \approx \log(0.007184) \)

The only problem here is that there is no decimal logarithm on the HP-12C keyboard. So in the code proposed by Gamo, several divisions by natural logarithm \( \ln(10) \) are used as a turn around to get the expected \( A = 10^{(0.425\frac{\ln(W)}{\ln 10 }+0.725\frac{\ln(H)}{\ln 10 }- 2.144)}\).

In order to spare steps and ease computation, I propose to directly compute the body area using the original formula.

Code:

Code:

001-   .725  y^x
006-   x<->y
007-   .425  y^x
012-   ×
013-   7184 EEX 6 CHS
020-   ×

Usage:
Press P/R to type the code in program memory. Go back to run mode and reset program to the start by pressing [GTO] 00 or [f][Program].

For each computation :
Type in Weight (in Kg) and press the [ENTER^] key.
Type in Height (in cm) and presse the [ R/S ] key to run code.
The HP-12C display the corresponding Body Surface Area in m².

This shorter code don't use any register or any logarithms. In fact, the logarithms stuff is done secretly by the y^x instructions.
Notice how old style RPN code are strange and 'reversed' as the second entered argument is treated first in the beginning of the code and the first entered argument is used last !