The book describes how logarithms are used in scales of measurement: for intensity of sound (decibel scale), intensity of earthquakes (Richter scale), level of acidity of a solvent (pH level), brightness of stars (absolute and apparent magnitude), ....The key properties of the log function are presented, those that make it so attractive and so indispensable in science-for describing population growth, radioactivity, cooling, etc. This book will be particularly useful to students who wish to appear for the Mathematical Olympiads.