Simple Statistics Program - need to chance

[Dinamarco]

Hi.
I'm using the program above.
But to end the entry of samples, needed to type "0"(zero).
Sometimes, 0 is a sample.....
Is possible to chance for and Letter? or other command?

Could somebody help me?

The program: (in line 5 and 13, it's necessary to chance, because on my HP41 program I just cannot insert the correct symbols)
I make some adjusts to use with a printer.

LBL "STAT"
FIX 3
BEEP
CLRG
"CL SIGMA" -----> key "F"
LBL 00
TONE 5
"ENTER DATA"
PROMPT
PRX
X=0?
GTO 01
"SIGMA +" --------> key "A"
STO 00
LBL 01
MEAN
XEQ 02
"MEAN="
XEQ 03
SDEV
CLA
XEQ 02
"SDEV="
XEQ 03
XEQ 02
RCL 16
1
-
SQRT
/
"SE="
XEQ 03
FIX 0
CLA
RCL 16
XEQ 02
"N="
XEQ 03
GTO "STAT"
LBL 02
TONE 9
TONE 9
RTN
LBL 03
ARCL X
AVIEW
FS? 55
RTN
STOP
RTN
.END.