World Metrology Day, celebrated on May 20 was established 7 years ago by UNESCO, Info-Prim Neo reports. According to “Moldova-Standard” Department, this day was chosen due to an event occurred 125 years ago. It marks the anniversary of the signing of the Metre Convention by 17 countries in 1875 at a conference in Paris. At that moment, the Convention was joined by 17 countries that had jointly worked out and started to use the Weights and Metric System. It had an important role for the metrology as science, because there were about 400 weight and 300 length units at the beginning of the XIX century. The use of different measurement units was inconvenient, so that people decided in 1875 to adopt a unique system of units. At present, the Agreement is signed by 37 countries of the world, members of the Metre Convention, which excludes technical obstacles in front of the free trade. The signatory countries win a major credibility in what concerns the performed measurements, and the issued certificates are recognised in all the countries of the world.