Which of the following is NOT a guideline for the proper use of an articulated ladder?

The correct choice highlights a critical safety principle regarding the use of articulated ladders. Using a box, barrel, or scaffold to gain additional height is not a recommended practice because it significantly increases the risk of falls and accidents. Articulated ladders are designed to provide stable access at various heights and should be used as intended, without any additional equipment that could compromise their stability or the user's safety.

The other guidelines—reading warning labels, wearing slip-resistant shoes, and facing the ladder while climbing—are vital safety measures that ensure proper use and prevent accidents. Reading warning labels helps users understand the specific limitations and instructions for the ladder, while wearing slip-resistant shoes provides necessary traction. Continually facing the ladder maintains balance and reduces the chance of losing grip or control while climbing. By following the correct safety guidelines, users can minimize risks associated with ladder use.