The floating point numbers used by LabVIEW are double precision (DBL) by default.

The old version of the function palette only has integer numerical constants. If you put it on the block diagram and directly enter 0.0 or the required floating point number, it will become a double precision.

You can also enter an integer and right-click and select "Representation", DBL.

The 2011 version has added "DBL numerical constants".