402 
THE MECHANISM OF BICYCLES. 
sequently in 144 revolutions of the star wheel (i.e. 720 revolutions 
of the bicycle wheel) the worm wheel rotates once. At the end 
of this one revolution a projection on the worm wheel comes 
into contact with one of the ten teeth on the “ unit ” wheel and 
moves the latter through a tenth of a circle and brings a fresh 
Diagram “ CThe Standard Cyclometer, 
figure in front of the aperture. When the unit wheel has completed 
one revolution a projection on it engages a tooth on the ten ” spur 
wheel, turns the latter through one tenth and brings a fresh figure in the 
second aperture. The same arrangement holds good with the 
“hundred” spur wheel. Two very light double springs press 
against ratchet faces on the backs of the spur wheels, acting as de¬ 
tents and so prevent any movement except when required and also 
