The ratio of the corresponding sides in triangles I and II is 1. We can interpret this ratio to mean that the sides of triangle II are 3 times the lengths of the corresponding sides in triangle I. We say that the number 3 is the scaling factor for these two similar triangles. Equivalently, we can say that the sides of triangle I are 1 times the length of the sides in triangle II, in which case the scaling factor is 1.Looking at triangles I and III, we can see that the scaling factor is 2. This scaling factor is similar to the way the power of a telescope or a pair of binoculars is described. If we are told that a telescope has a “100 power” lens, this means that the observed size of the object through the telescope is 100 times larger than the size of the object as observed with the naked eye. In other words, the image size has been scaled up by a factor of 100. Similarly, if a scale model of an airplane is built on a scale of 1, this means that 1 inch on the model represents 60 inches (or 5 feet) of the actual airplane.