Wheel calculator

A wheel calculator is made of concentric paper or plastic discs, used to make calculations involving time periods. They have applications in pregnancy (to calculate the due date) and insurance.

An Internet web site that may be used for insurance cancellation calculations provide the manual paper wheel calculators. The online wheel calculator can be used to calculate all three cancellation methods.

A circular calculator made out of paper and plastic disks that works similar to a circular slide rule. It has a base line that is aligned with the inception date of the insurance policy. An arm on the wheel is then aligned with the cancellation date of the policy. The number of elapsed days, pro rata and short rate factors, both earned and unearned, are indicated by the arm in proper column. The policy premium is multiplied by the factor to calculate either the earned or unearned premium.

...
Wikipedia