The method for displaying speed variables in a motor vehicle includes automatically selecting and displaying one of a number of different possible speed scales on a speedometer according to the physical units for speed values employed at the current location of the vehicle. An acoustic and/or optical alarm signal is produced when the vehicle passes from one governmental region in which one set of physical units is used to another in which a different set is used. In addition, speed limits at the current location may be displayed on the speed scale itself by highlighting an appropriate scale mark or producing a scale mark of a different length or color. The current location may be obtained from an on-board GPS. The speed limits and physical units for speed values at the current location are retrieved from a data storage media according to that location. The speed limits may be updated by radio connection. Digital display devices for speed values with similar features are disclosed.