Notes: "The Weems & Plath proportional dividers are unusual among proportional dividers: they are specifically for time-speed-distance problems rather than the usual scaling up/scaling down, dividing circles into polygons, etc. The dividers are designed so that once they are set, you can spread the points to a given distance on a chart and immediately read off time or velocity. In addition to scales specific to their primary purpose, time-speed-distance solutions, these dividers also have a scale from 1 to 10 for setting the enlargement/reduction ratio as with conventional proportional dividers. "
