Some standard ladders of DNA won’t form a perfectly linear standard curve. An example is attached. This is normal and can occur when there is a wide range of fragment sizes. In the case of Fig. 1, the bands range from 10,000 to 300 base pairs. The data is said to be “bimodal,” because the data fall into two somewhat linear sections. This is not a Logger Pro bug. It is simply a reality of gel electrophoresis.
The workaround is to create two files with separate analyses. First, select only the standard ladder bands that fall into the first bimodal section. You can tell you are nearing the end because the points will fall farther off the line. Identify the sample bands only in this upper region of high base pair numbers. Save the file.
Create a second Logger Pro file and select only the standard ladder bands that fall into the second bimodal section. Identify the sample bands only in this lower region. Save the file with a different name.
Between these two files, you will have all the information you need.