1. This was one of range of circular rules made by this Dutch company.

2. The rule has a single cursor. It consists of two discs, the outer one of which rotates. It is set in a metal box which when opened can double as a desk stand for the rule.

3. The rule has a spiral log scale printed on paper and fixed to the lid of the box.

4. The scales have a non-standard labelling system. Some of the gauge points, such as Cu, are not common.

4. The company also made specialised rules such as for mechanical engineers, reinforced concrete and timber calculations.