Schematic drawing of the tactile acuity charts containing dot patterns (A) and Landolt rings (B).

<p>Due to the micro-manufacturing procedure of the polymer material, the test patterns had to be fitted in a circular sheet. The size of the characters varied between lines from 0.0 (i.e., standard Braille spacing) to −0.5 log units for the dot patterns and from −0.3 to −0.7 log units for the ring patterns. The additional thermo-sensitive A4 paper versions also included lines with larger spacings up to +0.3 log units. All lines except those with the largest spacing contained 8 characters each.