Hyperbolic geometry or hypercycle, then the triangle has no circumscribed circle. As in spherical and elliptical geometry, in hyperbolic geometry if two triangles are similar, they must be congruent. A special polygon in hyperbolic geometry is the regular apeirogon, a uniform polygon with an infinite number of sides. In Euclidean geometry, the only way to construct such a polygon is to make the side lengths tend to zero and the apeirogon is indistinguishable from a circle, or make the interior angles tend to 180 degrees and the apeirogon approaches a straight line. However, in hyperbolic geometry, a regular apeirogon has sides of
Medvedev–Sponheuer–Karnik scale 1980s, the MSK scale became widely used in Europe and the USSR. In early 1990s, the European Seismological Commission (ESC) used many of the principles formulated in the MSK in the development of the European Macroseismic Scale, which is now a "de facto" standard for evaluation of seismic intensity in European countries. MSK-64 is still being used in India, Israel, Russia, and throughout the Commonwealth of Independent States. The Medvedev–Sponheuer–Karnik scale is somewhat similar to the Modified Mercalli (MM) scale used in the United States. The MSK scale has 12 intensity degrees expressed in Roman numerals (to prevent the use