Visual Acuity

(1)

where s = angular separation in minutes of arc between                          two lines or points which are just separable                          by the eye, minute

Example 1

A signwriter has to erect a nameboard with the letters BLC easily discernible from a distance of at least 1000 m. Allowing for average acuity of 2 and adding a safety factor of 2, determine the minimum height of the letters if the gap in the letter C is one-fifth the height of the letter.

Let the height of the gap be h meters after taking the safety factor of 2.

The letter height = 5h = 5 x 0.29 = 1.45 m