MercoPress. South Atlantic News Agency

Weights and measures conference to re-calibrate a kilogram

The kilogram prototype, made of platinum-iridium, has a diameter and height of 39 millimeters. The one at Tsukuba, one of 40 replicas made along with the original

Looking like a museum piece, a replica of the prototype to determine the exact unit of measurement for a kilogram was displayed under glass at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan.

 The Japanese replica is kept within a double glass container in a room with a temperature of zero to prevent mold from contaminating an accurate measurement.

The prototype, made of platinum-iridium, has a diameter and height of 39 millimeters. The one at Tsukuba, one of 40 replicas that were made along with the original, arrived in Japan in the late 19th century.

The replica was displayed ahead of Tuesday's, November 13 start of the General Conference on Weights and Measures in France that will discuss revisions for how weights and measures are defined.

Discussions about revising the kilogram began in around 1990 due in part to the inaccuracies that have arisen because of contamination of the prototype. Although the replicas kept in various nations have been stored under strict climate-controlled conditions, discrepancies of as much as 50 micrograms have been found in some replicas.

Under the new definition of the kilogram, the Planck constant will be used, doing away with the need for using the prototype and its replicas to measure mass. The Planck constant is a physical constant related to light.