The selected base unit cannot be used. It causes a looping conflict with another unit/base unit combination in this unit ...

The selected base unit cannot be used. It causes a looping conflict with another unit/base unit combination in this unit group. A loop is created when a unit is specified as the base unit for its own base unit. For example, a loop is created if Unit A is specified as the base unit for Unit B, and Unit B is specified as the base unit for Unit A. Select a different base unit and try again.