The box compass can only point north / south. They are used for orienting an instrument in the North / South line rather than indicating a heading. Often used with the theodolite when it is not a 'full' boussole theodolite for setting up a reference direction. Also used with the plane table and alhidade for setting up the chart to point to (magnetic) North. These devices do not have a setting for variation.
There are 2 products.