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Finally, in September 1982, Germany's standard-setting agency, Deutsches Institut für Normung (DIN), their equivalent of our American National Standards Institute (ANSI), relented and permitted the American Optical Airpuff Tonometer to be sold in Germany. However, increased labors from all technical nations are still needed. The Englishbuilt Perkins hand applanation tonometer cannot be sold in Germany. Neither our diopter nor our prism diopter exists in the International System of Units in the eyes of the International Union of Pure and Applied Physics. To the Germans, there is only the reciprocal meter (It's hard for me to write ophthalmic prescriptions in such terms.). Even the reference wavelength of monochromatic light used to measure what would be a diopter—a reciprocal meter—continues to be strongly championed by German optical scientists at the elegantly narrow mercury e line (546.07 nm according to the Draft International Standard [International Orgànization for Standardization/Draft International Standard (ISO/DIS)] 7944, Feb
Keeney AH. Update: International Standards 1983Ophthalmic Urgencies for 'One World'. Arch Ophthalmol. 1983;101(11):1685. doi:10.1001/archopht.1983.01040020687002