How should the Snellen exam be recorded if a driver identifies the line minus one letter?

The Snellen exam measures visual acuity and is generally recorded as a fraction, where the top number indicates the distance in feet at which the test is performed, while the bottom number indicates the distance at which a person with normal vision could discern the same line of letters. If a driver reads a line and identifies minus one letter, it signifies that they have slightly less visual acuity than that line’s criterion but are still able to read most of it.

In this case, when the driver reads 20/40 and is credited with identifying one letter less (minus one), it should be recorded as 20/40-1. This notation reflects that the driver can read line 20/40, but isn’t quite able to read the entire line due to misreading one letter. Thus, this notation gives a precise representation of the driver's visual capabilities in accordance with standard practices.