An interactive educational system includes a tracking system for determining changes in an overall physical location of a student, and a display for displaying cues for the student to engage in full-body motion and to engage in an interactive cognitive learning task. In this device, a digital pen is used to input data such as handwritings or graphic data instead of entering through a key pad of cellular phone, forming an e-mail, a brief message, a document, which may be locally stored or further transmitted to another cellular phone via transmitter station or via internet to overcome the disadvantage and limit of entering data from key pad of cellular phone. The oil quality parameter is used as an input to a calculator to determine a quantity of oil that must be replaced by fresh oil during a current maintenance outage in order to ensure that the engine oil quality will remain acceptable throughout a forthcoming operating period.