Interpretation ID: aiam1067
Bus and Truck Supply Co.
315 Continental avenue
Dallas
TX 75207;
Dear Mr. Graham: This is in reply to your letter of February 21, 1973, requesting tha we refer you to either the source or the size of letters used in the Snellen ratio 20/40, which is incorporated into S5.2.2 of Standard No. 217, 'Bus Window Retention and Release.' You state in your letter that you cannot find a source for the letter size required to meet the standard.; Snellen charts are those charts used generally by optometrists or othe persons interested in measuring eyesight. They are universally available from medical supply businesses. I point out that the standard does not require a specific letter size, as your letter implies, but only that a person whose vision has been measured to the specified Snellen ratio be able to read the exit identification required by S5.5. This legibility will be based not only on lettering size, but also on its contrast with its background, its shape, its precise location, and the configuration of the bus interior.; Yours Truly, Richard B. Dyson, Assistant Chief Counsel