[See also: Cats and Dogs May See in Ultraviolet] Like the human retina, the canine retina contains other kinds of photoreceptors in addition to cones, called rods. These light receptors do not perceive color, but they are sensitive to light and dark changes, as well as shape and movement. And the ratio of rods to cones in the retina is much higher in dogs than it is in humans.
The distance between rungs, cleats, and steps shall not exceed 12 inches and shall be uniform throughout the length of the ladder. 1910.27(b)(1)(iii). The minimum clear length of rungs or cleats shall be 16 inches.
Things You'll Need. 1  Measuring tape. 2  Measure all three aspects of ladder length using a tape measure. 3  Measure the length of an extension ladder against its duty rating.  Measure the distance between 1  rungs. Measure the width of the base and fly sections.