To prevent corrosion resistance of a rod from being weakened by composing an optically readable marking, of at least a part of a mechanical element provided with a surface having a first reflective force and a plurality of areas having a second reflective force.
An optically readable marking is provided on a mechanical element, once the foundation of the marking is placed in a prescribed diameter. An appropriate part of the mechanical element which is steel is covered with a bronze substrate. After the covering, the bronze substrate is so polished as to attain the surface finishing without showing any porous sign. The chrome surface is deposited on the bronze so as to form a surface 12a having a first reflective force. A prescribed area of the chrome is scanned and removed by laser to create a bronze exposed area having a second reflective force. The laser scans the circumference of a part of a rod circumferential part so as to mark the circumferential part on a plane perpendicular to the axis of the piston rod 12. The rod 12 moves axially by a minute distance and another area is scanned till an area having a prescribed width is formed.
SHEPHERD JOHN
BRASSINGTON ROGER WILLIAM
MOORE IAN ARNOLD
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