Folds, seams, tape, or any irregularity on the surface can also cause problems. An adjustable tracer arm allows use on a variety of different maps. They are more accurate because the shortest arm length can be selected for each application, and shorter means more accurate. This is the smallest area which can be traced and still record on the measuring dial and vernier. The smaller the number for resolution, the more precise the measurement will be when tracing small features.
Digital planimeters are available in both styles, while mechanical planimeters are only pole style.
The roller is easier to use when tracing areas which are very long or tall. This prevents having to make multiple measurements because of having to reset the pole arm. Many consider a roller type as easier to use, but it's really personal preference. Range is determined by the length of both the pole arm and tracer arm. It tells the maximum actual area which can be traced at one time.