Don’t forget that the classic vector diagram for course to steer in a cross-tide is worked on proportions. It is conventional to let one mile be the scale for one knot. This of course is measured from the latitude scale on the chart. It is equally correct, however, to use any convenient scale at all. You could use longitude, inches, centimetres, or the length of your thumbnail. All will give the same answer.
The scale on the side of a Breton Plotter can often be pressed into service, a system used by old hands for many years. There is, however, one item to remember. If you draw a parallel to your course to steer so that it passes through the destination, the length of the line gives the actual distance to sail and hence the required material to work up an ETA. To measure it, however, you’ll have to go back to good old minutes of latitude, because speed is still measured in mile per hour.