Field's parallel rulers are made in two forms, one rolling and the other sliding.
I pricked that place off on the chart with my dividers, and with my parallel rulers found that west-by-south was the true course.
It is just as accurate, too, if you lay the distances off carefully with the dividers and parallel rulers.
Captain Ponsberry said no more, but threw down his parallel rulers and his pencil.
The parallel rulers need no explanation except for the way in which they are used on a chart.