1,500 years ago the first distance recording-chariot , the Odometer Drum Chariot , was made in China . Its mechanical 
principle is the same as the later odometers .
The earliest historical record of the Odometer Drum Chariot was found in the “Jin History : Chariot and Clothing”. It stated : “A standing wooden figure hold a mallet above a drum , striking the drum once whenever the chariot travels a li .” In the “Song History” and the “Sui History” there are basically similar records . In the annotations to the “General Code” there was a supplementary record (quoted from the “Annotations to the Ancient and Contemporary Works” compiled by Cui Bao in the Jin Dynasty ) ;
The Big Decorative Chariot , also known as Distance Recording Chariot , was seen first in the Western Capital . It had two levels with a wooden figure on each level . When the chariot traveled one li , the wooden figure on the lower level struck a drum . When the chariot traveled ten li , the wooden figure on the upper level struck a gong .
A ceramic model ship in the Eastern Han Dynasty was unearthed in ceramic modern ship in the Eastern Han Dynasty was unearthed in Guangzhou . An axial rudder was found at its stern . It was transitional from the long oar rudder to the axial turning rudder . Between the second and fourth centuries A.D. , the true axial turning rudder was used already in China , 
which was important for raising ship-operating efficiency . In about the twelfth century A.D. both the water-tight compartments and the axial turning rudder spread westward to the Mediterranean via the Indian Ocean . In the eleventh century A. D. the Chinese already invented the balance rudder and the holed rudder , both of which were only found in Europe at the eighteenth century A.D.
The knack of the distance-recording chariot lay entirely in the clever utilization of the wheels and gears . 
On the chariot were mounted two coaxial ground wheels with a diameter of six feet ( of ancient measurement ) . On the left ground wheel was attached an 18-tooth vertical wheel . At right angle with this ground wheel was attached a 54-tooth lower horizontal wheel . Over the lower horizontal wheel was mounted on the same axle a 3-tooth whirling wheel , which engaged with a big right horizontal wheel with 100 teeth . On the big horizontal wheel were attached on the same axle a pair of iron picks . When this big horizontal wheel revolved one cycle , the iron picks . would stir once two twisting picks connected to the arm of the wooden figure by pulleys and ropes . As the chariot covered a distance of 300 steps , or one li , the ground wheel had turned 100 cycles , and the big horizontal wheel had just come to the point where the iron picks stirred the twisting picks . Then the ropes moved the wooden figure to strike the drum once . This audio signal meant that one more li was covered . So , a cycle for distance-recording was completed .
In a word , he distance-recording chariot realizes a fairly high generalizing capacity for measuring the distance it has covered . With its mechanism , it transforms the distance measurement to audio signals . The whole course of distance recording involves coordinated space traveling , mechanical movement and perception transformation . In the history of science , it has been regarded as an intelligent ancient invention that applied most successfully the gear deceleration principle .
