  We consider Chorin-Temam scheme (the simplest pressure-correction projection
method) for the time-discretization of an unstationary Stokes problem. Inspired
by the analyses of the Backward Euler scheme performed by C.Bernardi and
R.Verf\"urth, we derive a posteriori estimators for the error on the velocity
gradient in L2 norm. Our invesigation is supported by numerical experiments.
