The relationship between the tracing speed and the low frequency (long wave) cutoff is mathematically expressed by the following formula:  

b. Amplification selection that establishes different ratios between the average value of the stylus excursions and the length of the scale. Depending on the type of the instrument there might be up to seven scale selections, ranging, for example, from 3 to 3000 microinches, although shop type instruments usually cover a narrower amplification range only, and offer a lesser number of rates.  

Additional selections and connections are also available on certain types of amplifiers, such as a changeover from Roughness average (Ra) to root mean square (RMS) values and a recorder connection.  

The meter is usually part of the amplifier, with the dial located on the front face of the instrument. Most meters indicate continuously, the momentary average-roughness value of the traced surface. Integrating type meters are also available with certain types of instruments, to show a single average value at the end of the trace covering a controlled traverse length. This is a fixed value that does not have to be estimated as the predominantly appearing pointer position, consequently, it offers a higher degree of repeat accuracy of the readings than those from even a well-damped, continuously averaging meter. Integrating meters, however, require more sophisticated instrumentation, and the available straight line traverse length must be at least five times, preferably, seven times the selected cutoff length.