Returns the value of an existing global variable of the client terminal. There are 2 variants of the function.
1. Immediately returns the value of the global variable.
2. Returns true or false depending on the success of the function run. If successful, the global variable of the client terminal is placed in a variable passed by reference in the second parameter.
[in] Global variable name.
[out] Target variable of the double type, which accepts the value stored in a the global variable of the client terminal.
Global variables exist in the client terminal during 4 weeks since their last use, then they are automatically deleted.