From Bright Pattern Documentation
Set Variable
This block sets a value for a scenario variable.
Settings
Variable name - The name of the variable.
Value – The desired variable value. Variables in the $(varname) format can be used as values. Values can be specified either as literal strings or expressions. Literal strings are passed exactly as entered. Expressions must begin with assignment sign = as the first character. For example, 2+2 will produce 2+2, whereas =2+2 will produce 4. Expression result produces one of the following data types: strings, integers and floating point numbers.