rotate back to its home position during which time constant speed was maintained with a centrifugal governor. Dials at user stations typically produced pulses at the rate of ten pulses per second (pps), while dials on operator consoles on Crossbar or electronic exchanges often pulsed at 20 pps. The rotary dial governor is subject to wear and aging, and may require periodic cleaning, lubrication and adjustment by a telephone technician. In the video, the green LED shows the dial impulse pulses and the red LED shows the dial's off-normal contact function. Off-normal contacts typically serve two additional functions. They may implement a shunt across the transmitter circuit and induction coil to maximize the pulsing signal of the dial by eliminating all internal impedances of the telephone set. Another function is to short-circuit the telephone receiver during dialing, to prevent audible clicking noise from being heard by the telephone user. Dials located in handsets Some telephones include a small dial built into the handset, with a movable finger stop. The user rotates the dial clockwise until the finger stop ceases moving, then releases both. In this design the holes extend around the full circumference of the dial, allowing a reduced diameter. This was introduced by Western Electric on the compact Trimline telephone, the first to locate the dial in the handset. In Spain, such phones were manufactured for CTNE (Compañía Telefónica Nacional de España) by Málaga-based factory "CITESA", being named as "Góndola" phones by its particular shape. Spanish Góndola sets were fitted from the beginning with a red LED series connected with the line, allowing the dial ("disco" in Spanish) to be backlit while dialling. For that, the LED was bridged by an anti-parallel Zener diode, to allow the DC to pass even if the line polarity were reversed. In case of line polarity reversal, the LED would not light, but the phone would work anyway. The LED and Zener diode were contained in the same package for ease of assembly in manufacturing. Britain In the United Kingdom the letter "O" was combined with the digit "0" rather than "6". In large cities the seven-digit numbers comprised three letters for the exchange name, followed by four numbers. Australia Before 1960 Australian rotary dial telephones had each number's corresponding letter printed on a paper disc in the centre of the plate, with space where the subscriber could add the phone number. The