At low frequencies, when 09 is less than about 0.1/z, the phase angle is virtually 0 ~ At high frequencies, when 09 is more than about l O/z, it is virtually-90 ~ . Between these frequencies the phase angle can be considered to give a reasonable straight line. The maximum error in assuming a straight line is 5ı8~9 When co = 1/z then the phase angle is 45 ~ Table 5.1 gives the errors in using the asymptotes.