These tools are used to establish concentricity and reduce run-out on revolving tool shafts, such as lathes and drills. They can also help detect bearing play. Good concentricity reduces heat and allows higher feed speeds and more accurate machining, can extend cutter and bearing life.
They are both in excellent condition.
They work together as a set (you need both), and are being sold as a set. Some instruction will be provided to the buyer.