  We study the order-disorder transition of the two dimensional interacting
monomer-dimer model (IMD) which has two symmetric absorbing states. To be
self-contained, we first estimate numerically the dynamic exponent $z$ of the
two dimensional Ising model. From the relaxation dynamics of the magnetization
at the critical point, we obtain $\beta/(\nu z) = 0.057~650(12)$, or $z = 2.168
26(45)$, where $\beta = \frac{1}{8}$ and $\nu=1$ are exactly known exponents.
We, then, compare the critical relaxation of the order parameter at the
transition point of the IMD with that of the Ising model. We found that the
critical relaxation exponent $\beta/(\nu z)$ is in good agreement with the
Ising model, unlike the recent claim by Nam et al [JSTAT {\bf (2014)}, P08011].
We also claim that the Binder cumulant is not an efficient quantity to locate
the order-disorder transition point of the model with two symmetric absorbing
states.
