| Description | Logarithmic chart uses traditional Sloan optotypes. These calibrated optotypes blur at threshold and adhere to the Snellen 5x5 grid. Sloan chart uses two smaller groups for repetitive testing and minimizes memorization. Logarithmic Sloan acuity | The charts come as a set of two panels (21x24inches, 53x60cm) each with a high contrast chart one side and a low contrast chart (18% Weber or 10% Michelson) on the other. The optotype set is the family of ten British Standard (1968) 5x4 non-serifed |