Tim,
The Rhino can move one step in any direction and stop on that square (same
as a non-royal king) as well as turning 45 degrees in the appropriate
direction and moving a second square. The non-royal King move alone is
worth 2 atoms. If the second move comonent if it were a leap would also
be 2 atoms. To allow for lameness, mutiply by .7, so add 1.4 atoms for
this component for a total of 3.4 atoms. The piece is substantially
stronger than a Rook.
You may be confused by some incarnations of the Rhino requiring the first
step to be orthogonal -- such a piece is indeed worth only 1.7 atoms, less
than a Knight.