Great Clock facts

Clock dials

Number of clock dials: 4
Clock dials diameter: 7m
Length of hour figures: 60cm
Clock dial frames: cast iron
Glass in each clock dial: 324 pieces of pot opal glass
Illumination of each dial: 28 energy efficient bulbs at 85 watt each
Lifetime of each energy efficient bulb: 60,000 hours

Minute hands

Material: copper sheet
Weight: 100kg, including counterweights
Length: 4.2m
Distance travelled by minute hands per year: equivalent of 190km

Hour hands

Material: gun metal
Weight: 300kg including counterweights
Length: 2.7m

The hour figure of 4 o'clock is shown by the Roman numeral IV, rather than the usual IIII on other clocks.

The mechanism

Clock mechanism frame material: cast iron girder frame
Clock mechanism dimensions: 4.7m long and 1.4m wide
Clock mechanism weight: 5 tonnes
Pendulum length: 4.4m
Pendulum weight: 310kg
Duration of pendulum beat: 2 seconds

Pendulum adjustment: pre-decimal pennies are used to regulate the clock mechanism. Adding one penny causes the clock to gain two-fifths of a second in 24 hours.

'The Double Three-legged Gravity Escapement', designed by Edmund Beckett Denison, compensates for outside pressure (like the wind) on the clock hands and is crucial for accuracy.

The pendulum bob

Pendulum bob weight: 203kg
Material: concentric tubes of steel and zinc