Traditionally the field of microscopy has centered on the creation of highly magnified images of things too small to be seen with the eye alone. This was certainly the case with scanning probe microscopy, which burst on to the scene some 15 years ago with dramatic images of individual atoms. We are visual beings and the rapid acceptance of SPM followed directly from its ability to represent physical interactions in an intuitive image format. However, much of the vaiue of SPM today derives from its ability detect and measure a wide variety of specific interactions between its scanning probe and the sample. As the technology continues to mature, emphasis is shifting from its ability to display these signals as images to its ability to quantify and measure them.