- Till now, the kilogram is the only one among units of measures pegged to real object.
- It was pegged to a cylinder (shown in fig) made up of 90% platinum and 10% iridium (In India, salt-shaker-sized cylinder weighing exactly a kilogram in National Physical Laboratory was used as ideal measure of kilogram since 1957.
- It was serving as reference for variety of industries to keep their weights accurate.
- But this cylinder’s weight in kilogram is known to fluctuate due to surface contamination with time, making it tricky to define its exact mass.
- The new measure for kilogram from 2019 will be derived from constants of nature that are all interdependent.
- It will be set by value of Planck constant in combination with definitions of meter and second.
- Kibble balance will be used to make accurate measures of Planck constant.
- Kibble balance is set of scales, which uses force produced by current-carrying wire in magnetic field to balance weight of mass.