The theory behind the "good" and "bad" length designations are based on impedances that are friendly to built-in autotuners vs impedances that are unfriendly to built-in autotuners. The "good" lengths are in the vicinity of the current maximum points on the ladder-line where the 50 ohm SWR is lower than 3:1. The "bad" lengths are in the vicinity of the voltage maximum points on the ladder- line where the 50 ohm SWR is very high. The unzipped, ready to run, 31kB DOS "IMAXMIN.EXE" file can be downloaded from: IMAXMIN.EXE
The BASIC source code for the above program can be downloaded from: IMAXMIN.BAS
A DOS graphic presentation of the current maximum points can be downloaded from: IMAXGRAF.EXE
A later version of this program shows the band edges but may be a little too busy for some tastes. For what it's worth, here it is: IMAXGRA2.EXE
These DOS programs will run under XP and earlier versions of Windows. For later versions of Windows, an X-86 simulator program called DOSBox is available for download on the Web that allows a DOS program to run in a window. One advantage of DOSBox is that screen capture of the graphic is easy.