Re: roller plotter or parallel rulers?
The problem with both rolling plotters and parallel rules is that in a moving boat, they tend to slide. A minor slide and you screw up your plotting. My solution (not patented yet) is to use a rolling plotter, I use an inexpensive Weems & Plath. They have two small grooves between the rollers. Go to Home Depot, and buy the smallest o ring that will fit snuggle in those grooves. Now you have a roller that stick to the chart. Good luck