>How the VtChLocationTypeCustom constant location works ?
>Does I need to define the top and left positions somewhere ?
>Thank you.

Yes Marc,
You have to define. Location has a Rect property that points to its Rectangle. It has min.x, min.y, max.x, max.y properties. When setting keep in mind it doesn't use the screen coordinate system we're accustomed to but map system :) That's y=0 is bottom line of control not top :

* Put legend in top-right or bottom-right
lparameters tlTop
With ThisForm.MsChart
  lnCurHeight = .Height * 15
  lnCurWidth = .Width * 15
  With .Legend
    .Location.Visible = .t.
    .Location.LocationType = 8
    With .Location.Rect
      lnHgt = .Max.Y-.Min.Y
      lnWdt = .Max.X-.Min.X
      .Max.X = lnCurWidth
      .Min.X = lnCurWidth - lnWdt
      .Min.Y = iif(tlTop, lnCurHeight - lnHgt, 0)
      .Max.Y = iif(tlTop, lnCurHeight,lnHgt)
    Endwith
  Endwith
Endwith

PS: Chart uses points not pixels. 15 comes from 1440/96. 96 is aspect ratio (normally you'd want to get that from GetDeviceCaps api). 1440 is twips per inch and 1 pt=20 twips.
Cetin