Gray (unit)
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The gray is the unit of ionizing radiation dose in the International System of Units (SI), defined as the absorption of one joule of radiation energy per kilogram of matter.
Using early Crookes tube X-Ray apparatus in 1896. One man is viewing his hand with a fluoroscope to optimise tube emissions, the other has his head close to the tube. No precautions are being taken.
Monument to the X-ray and Radium Martyrs of All Nations erected 1936 at St. Georg hospital in Hamburg, commemorating 359 early radiology workers.
International System of Units
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The International System of Units, internationally known by the abbreviation SI, is the modern form of the metric system and the world's most widely used system of measurement. Coordinated by the International Bureau of Weights and Measures it is the only system of measurement with an official status in nearly every country in the world, employed in science, technology, industry, and everyday commerce.
Silicon sphere for the Avogadro project used for measuring the Avogadro constant to a relative standard uncertainty of 2×10−8 or less, held by Achim Leistner
Stone marking the Austro-Hungarian/Italian border at Pontebba displaying myriametres, a unit of 10 km used in Central Europe in the 19th century (but since deprecated)
Closeup of the National Prototype Metre, serial number 27, allocated to the United States