The shape of a ships hull is such that there is a more space for planking between the rail and the keel
for planking strakes at some points along the hull than at others. To fit the same number of planks in
that space, each planking strake must be shaped to differnet widths along its length. The planking gauge
acts as a proportional divider to work out the width of each planking strake at various points chosen
by the model builder.
