1. Principles of Measurement

2. Early Measurement Egyptian measurement
Phatom = length of rope a man could hold between his out stretched hands
Cubit =distance from bent elbow to tip of middle finger approximately 500mm
Chinese measurement
Shaku = distance from edge of thumb to tip of middle finger on outstretched hand

3. Birth of Metre
Invented by two French astronomers Jean Delambre and Pierre Mechain in 1799.
They decided that to provide accurate measurement a standard consisting of a physical constant was required. ‘A tous les temps, ‘a tous les peuples’ (for all time for all people).
They decided that this standard should be related to the dimensions of the earth.
It was eventually decided that it would be related to a segment of the earth a in straight line running from the north pole to the equator which passed through Paris

4. Jean Delambre set off from Dunkerque heading south Pierre Mechain set off from Barcelona heading north and they met in Paris a journey which took more than six years.
They each used triangulation to measure the distance they had travelled to obtain an accurate measurement.
From this they were able to calculate the distance from the north pole to the equator in a straight line through Paris
This distance was divided by
and became the standard unit of length called the metre which we use today.

5. Below is the prototype Metre produced from 90% platinum 10% Iridium which became the international line standard for measurement which is used today

6. Glass Zerodur Line standard

7. The Helium-Neon Laser Interferometer
Wave length of Helium-Neon laser Beam = mm

8. Units