1. A vehicle diagnostic system comprising: a processing unit for coupling to a vehicle, the processing unit for executing instructions and for receiving signals from a vehicle; a long-term memory, coupled to the processing unit, the long-term memory storing instructions to be executed by the processing unit and storing display values capable of being translated into a perceivable output, the instructions to be executed by the processing unit including coding objects of a first type, the coding objects of the first type capable of calling other coding objects of the first type during execution, each coding object of the first type having a state field and the coding object of the first two returning a state from the state field without executing when the state field indicates that the coding object has been previously executed; a random access memory, coupled to the processing unit, the random access memory for receiving a copy of instructions stored in the long-term memory to form a source of instructions for the processing unit to execute, at least one coding object of the first type copied into the random access memory including a reference to a display value stored in the long-term-memory; and a user interface, coupled to the random access memory, the user interface for retrieving display values from a portion of the random access memory and for creating a perceivable output based on the retrieved display values.