Logmar 4m ETDRS Number Chart 4 metre viewing. Acuity range 40m to 2M. Will fit illuminated cabinets SDT-392-LSV and SDT-396-LPV These Original Charts - Are the only standardised format acceptable in studies sponsored by the American National Eye Institute. They were designed for use in clinical studies and low vision evaluations where accurate, repeatable visual acuity measurements are required. The lines are of equal difficulty and geometrical progressions, in number, from line to line.