=SI(A3="";"";SOMMEPROD(DECALER(C3;1;;EQUIV("";""&DECALER(B3;1;;;100);0))))
Function SommePartielle(ColProduit As Range, ColPrix As Range)
Dim lig&, n As Variant
lig = Application.Caller.Row
n = Application.Match("*", ColProduit(lig + 1).Resize(ColProduit.Count - lig), 0)
If IsError(n) Then n = ColProduit.Count - lig
SommePartielle = Application.Sum(ColPrix(lig + 1).Resize(n))
End Function
=SI(A3="";"";SommePartielle(A:A;C:C))