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In 1881, the International Electrotechnical Exhibition opened in Paris, and the First International Congress of Electricians was held. At both conferences, the issue of international units of measurement was discussed.

 

At this congress, it was decided to link electrical units with a common system of measures and weights, the gram-meter-second system. To link the electrical system of measurements with the common system of measurements, it was necessary to compare electrical forces and gravitational forces. Special scales were built for this purpose.

 

One coil is suspended from the scale pan. The other coil, fixed, is attached to the box in which the scale stands. An electric current is passed through the coils. Then, they are attracted to each other. The attractive force of the coils was balanced by weights placed on the other pan. This is how precise reference measurements of currents were made. However, scales with pans are not the most convenient instrument for measuring. Nowadays, in trade, scales with pans are increasingly replaced by spring scales with arrows. For electrical measurements, the current strength began to be balanced by a small spring - this is how the now generally accepted design of an electrical measuring device was established.