  We prove an improved Pleijel nodal domain theorem for the Robin eigenvalue
problem. In particular we remove the restriction, imposed in previous work,
that the Robin parameter be non-negative. We also improve the upper bound in
the statement of the Pleijel theorem. In the particular example of a Euclidean
ball, we calculate the explicit value of the Pleijel constant for a generic
constant Robin parameter and we show that it is equal to the Pleijel constant
for the Dirichlet Laplacian on a Euclidean ball.
