Bill,
I have found the problem. I mistook the meaning of LN=xxx under the > MEM , PROGRAMS menu. I thought this was the check sum, but it is not. I suppose it is memory used by this label. Here is the code anyway, you may already have it, but I have updated it since I first posted it:
Eric Lundgren April 2005
Rev 2  August 2005
HP 33s/ Location of Vertical Nuetral Axis, and Ix (Second Moment)for composite cross section:
Description: For a buildup of n rectangular sections (ibeam, cchannel, sandwich, etc.), this program computes the location of neutral axis (measured from bottom of section), and the moment of inertia.
To use the program
The program requires that FLAG 1 is set prior to running. I simply keep FLAG 1 set all the time.
Execute via XEQ I, and you are prompted for number of sections. A basic Ibeam would have 3 sections (web, upper cap and lower cap). B = width of a section, and H = height of that section.
Both lines of the screen are used for the result:
Upper line is the location of vertical neutral axis (centroid). Lower line is the second moment of inertia of the plane area defined by the combined rectangular sections. Note that you can model two plates that have open space between them (perhaps a foam core that does not contribute to stiffness) by entering the width as zero, and then height equals the empty space.
LBL I
FS? 1
CLVARS
FS? 1
INPUT N
CF 1
INPUT B
INPUT H
RCL H
2
/
RCL +T
RCL B
RCL * H
*
RCL +Q
STO Q
RCL B
RCL H
*
RCL +R
STO R
1
RCL +V
STO V
RCL Q
RCL / R
RCL – C
X^2
RCL *A
RCL + I
STO I
RCL T
RCL H
2
/
+
RCL Q
RCL / R

X^2
RCL *B
RCL *H
RCL H
3
Y^X
RCL *B
12
/
+
RCL + I
STO I
RCL Q
RCL / R
STO C
RCL B
RCL * H
RCL + A
STO A
RCL T
RCL +H
STO T
RCL V
RCL N
X>Y?
GTO I
SF 1
RCL C **location of neutral axis**
RCL I **value of composite Ix **
RTN
CK: 1A60(valid only on HP33s)
LN = 270