National Physical Laboratory of India is realized by using an absolute radiometer. For practical work, a group of tungsten incandescent lamps are used. The level of uncertainty is ± 1.3 × 10. Experimental work has been initiated to realize mole, the SI unit for amount of substance The NPL does not maintain standards of measurements for ionizing radiations. This is the responsibility of the Homi Bhabha Atomic Research Centre, Mumbai. The standards maintained at NPL are periodically compared with standards maintained at other National Metrological Institutes in the world as well as the BIPM in Paris. This exercise ensures that Indian national standards are equivalent
British thermal unit British thermal unit The British thermal unit (Btu or BTU) is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is part of the United States customary units. Its counterpart in the metric system is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius. Heat is now known to be equivalent to energy, for which the SI unit is the joule; one BTU is about 1055