Considering strength was not an problem when BS680 was written seventy years ago; a strength check was not included and this has been a downside in the face of weak imported slates. Happily; the new standard deals with this issue. Firstly; that heavy metal strength; the ?modulus of rupture?; are measured on a trial of 40 test pieces and from this specific strength score together plus across the slates have always been determined. These kinds of values can then be applied to an equation which gives a minimal standard slate width; ebi.