The unit vector in the .stl file

Hello,

I am writing the code to convert a mesh of square surfaces to a .stl file. I am using 2 triangles per square and have been successful in generating .stl files.

The problem is that each facet in my .stl file looks like this:

    facet normal 
        outer loop
            vertex 0.0390000008 0.0280000009 0.0500000007
            vertex 0.0399999991 0.0280000009 0.0500000007
            vertex 0.0390000008 0.0280000009 0.0489999987
        endloop 
    endfacet 

There is no unit normal specified, with the outer surface just selected using the right hand rule.

What is this unit normal exactly supposed to be?
Is it a vector with origin at the triangle's centroid, of magnitude 1, that points in the direction of the positive normal to the plane of the triangle?
Also, since it's a floating point number, does any parser just select the normal that is closest to what is described by this vector?

I have imported models to Solidworks and Blender and have not had issues with not specifying the normal vector.