Richter scale
noun
Rich·ter scale ˈrik-tər- 
: an open-ended logarithmic scale for expressing the magnitude of a seismic disturbance (such as an earthquake) in terms of the energy dissipated in it with 1.5 indicating the smallest earthquake that can be felt, 4.5 an earthquake causing slight damage, and 8.5 a very devastating earthquake
Word History
Etymology
Charles F. Richter
First Known Use
1936, in the meaning defined above