Abstract: A navigation system provides advice to a driver of a battery electric vehicle regarding charging a battery mounted in the battery electric vehicle. The navigation system includes an input device, a storage medium, a measurement device, and a controller. The input device is configured to receive an input of a normal state during driving in advance by the driver. The normal state during driving is recognized by the driver. The storage medium is configured to store the normal state received by the input device. The measurement device is configured to measure a current state during driving. The controller is configured to calculate a difference between the normal state stored and the current state measured, and set the advice according to the difference to provide the driver.

Abstract: A disturbance degree calculation system includes a sensor that acquires data on a factor that hinders safe driving of a driver, and a disturbance degree calculation unit that calculates a disturbance degree indicating a degree of disturbance to the driver's safe driving based on the factor hindering the safe driving of the driver.