The LM and UM refer to the Lower Marker and Upper Marker. They are spike-in controls that are used to determine the size and/or concentration of your sample.

The Basics of a DNA run:
The Fragment Analyzer results file has an electropherogram of the sample and a gel image. The upper and lower markers and are used for alignment. The markers also help calculate the concentration of your sample. The peak sizes, concentrations, and molarities are listed beneath the electropherogram.
Below the first set of results there is another set of results based on the “Smear Analysis”. Results listed in the Smear Analysis section are based on everything in the area of the curve between the two vertical dotted lines. The Y-axis is fluorescent units, so the higher the peak the higher the concentration is for that particular nt size.

Characteristics of a Good Run:
Features to look for in a good run are flat baselines, well resolved peaks, and the presence of the upper and lower marker. All sample peaks should appear between the lower and upper marker peaks.