  Let $(K,v)$ be a valued field, and $\mu$ an inductive valuation on $K[x]$
extending $v$. Let $G_\mu$ be the graded algebra of $\mu$ over $K[x]$, and
$\kappa$ the maximal subfield of the subring of $G_\mu$ formed by the
homogeneous elements of degree zero.
  In this paper, we find an algorithm to compute the field $\kappa$ and the
residual polynomial operator $R_\mu : K[x]\to\kappa[y]$, where $y$ is another
indeterminate, without any need to perform computations in the graded algebra.
This leads to an OM algorithm to compute the factorization of separable
defectless polynomials over henselian fields.
