Numerical variables can range from %0～%999 -- 1000 total.
0-199 are general variables, and 200-999 are globals.
General variables are reinitialized upon game restart, reset, or many other things, but global variables retain their values.
In other words, general variables are saved and loaded on savetime and loadtime, but global variables remain constant throughout.
Therefore, it's best to use general variables when doing math, and to use global variables for things like clear flags, etc.
If you wish to use global variables, you'll have to specify the command globalon in the definition block somewhere.
The default value of a numerical variable is 0.