Should'nt global variables be available to subroutines?

[Gene222]

I got my HP Prime two week ago, so I am kinda new at this. I started working on a program with a subroutine, but the subroutine would not work unless all variables used in the subroutine were pass to the subroutine when I called the subroutine. Should not the global variables (in this case Q, N, D, and S) be accessible for use by the subroutine? Am I doing something wrong with my code? I though global variables and system variables (A through Z) were supposed to be accessible to all programs.

My other question is do I need to declare system variables A through Z in any program that uses those variables? I find the concept of system variables, local variables and export command somewhat confusing.

Thanks, Gene

My program thus far:[/code][/php]

Sub1();

// Main program
local X1, X2, FX1, FX2;
EXPORT Pipe(Q,N,D,S)
BEGIN
input({Q,N,D,S},
"Pipe Flow",
{"Q cfs = ",
"n value = ",
"Dia ft = ",
"Slope ft/ft = "});
// Initial X values where X = y/D
X1:=0.5;
X2:=0.8;

// Determine f(x1)
FX1:=Sub1(X1,Q,N,D,S);
print (FX1)

END;

// Subroutine to calc f(x)
Sub1(X,Q,N,D,S) //Why should Q,N,D,S need to be included?
BEGIN
local theta, A, R;
theta:= acos(1 - 2*X);
A:= (D^2 / 4) * (theta - 0.5*sin(2*theta));
R:= (D/4) * (1 − sin(2 * theta) / (2*theta));
return (1.486/N)*A*R^(2/3)*S^(1/2) - Q;
END;