A grille is an air terminal device with multiple passages of airflow. A register is a combination of grille and damper assembly.
Clamp meter connected to an AC monitors the current flow and indicates usage (range) through green, orange and red colour codes. The four friends had learnt about capacitor and its use in many electronic appliances in their physics class. Ageing of these, leads to lesser efficiency of the appliance. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.