  The R algorithm is widely used for simulating two flavours of dynamical
staggered fermions. We give a simple proof that the algorithm converges to the
desired probability distribution to within O(dt^2) errors, but show that the
relevant expansion parameter is (dt/m)^2, m being the quark mass. The Rational
Hybrid Monte Carlo (RHMC) algorithm provides an exact (i.e., has no step size
errors) alternative for simulating the square root of the staggered Dirac
operator. We propose using it to test the validity of the R algorithm for
simulations carried out with dt m.
