These proportional dividers were useful in transferring detail from one scale of drawing to another. For example, a large scale plan at 1:2500 is four times larger than our target drawing scale of 1:10000, a 1:4 ratio requiring a setting of 400 on the proportional divider scale. Alternatively, if the national grid was marked on a plan, a map roamer was used with the small scale map to accurately transfer detail.