  The aim of this paper is mainly, after some theoretical explanations, to
provide a program on Maple for computing, whatever be d, the curvature of the
planar d-web implicitely defined by a differential equation F(x,y,y')=0, F
being polynomial of degree d with respect to y'.
  Moreover, we prove in the appendix a "concentration theorem" for any
calibrated ordinary $d$-web of codimension one in n-dimensional manifold (in
particular for any planar web). Its curvature matrix, relatively to an
"adapted" trivialization, is concentrated on the (n-2+k0)!/(n-2)!k0! last lines
(the last line if n=2), k0 denoting the integer such that
d=(n-1+k0)!/(n-1)!(k0)!$.
