The Double Parameter Form includes a Double tab.
Use the Double field on the Double tab to specify the IEEE double-precision (64-bit) floating point number that the Parameter is to store.
You might, for example, use a Double Parameter to store the target value for one or more analog points, and include that target value in a series of Logic programs. Such configuration is particularly useful on systems in which Logic program(s) are included in Group Templates, and the target value differs in some Instances of those program(s).