The internationally adopted system of measuring surface texture is to use the roughness average parameter designated Ra. In order to choose the optimum roughness average level, consider tolerance required as shown in Chapter 6 and Table 5-3. Cost or machining time increases with finer surfaces as shown in Fig. 5-3. A typical relationship of surface texture and production time (cost) is shown in Fig. 5-3. The chart, Fig. 5-3, shows a series of curves displaying production time in relation to Ra values for the range of common machining processes, and is based on research carried out on machine tools from 1 to 10 years old. The chart, however, is not intended to be used for making comparisons between different processes. Results obtained from common production processes in terms of Ra values (micrometers) are shown in Table 5-4. [Note: Tables omitted from Abstract.]