Variables

1.

Define the name of the new variable in extend.h:
For example #define TOLERANCE_VARNAME "tolerance"

2.

Define its default value:
#define DEFAULT_TOLERANCE 0.5

3.

Declare it as an extern variable:
extern double Tolerance;

4.

``Create'' it with CreatexxxVariable in extend.c:InitExtension, where (xxx) is the desired type. There are macros for several types defined in misc/shell.h.