An on board vehicular data processing system samples vehicular operating parameters such as fuel level, distance travel, etc. The system calculates values of other parameters such as range and travel time. Under control of the position of the ignition key, which assumes positions representative of modes of operation, OFF, PARK, TRIP, START, the system displays indications of a limited number of sensed and calculated parameters, the particular indications being those which are most useful for the instant mode of operation represented by the position of the ignition key. After a trip, system parameters may be stored for future reference by a predetermined sequencing of the ignition key position. Such storage may be cleared by a second sequencing of the ignition key positions. Parameter reference values may be stored as maximum or minimum and present values for a parameter may be compared with the maximum or minimum and an alarm indication given, acoustical or optical.