Some electronic devices are marketed as fuel savers. The Fuel Doctor FD-47, for example, plugs into the vehicle's cigarette lighter and displays several LEDs. It is claimed to increase vehicle fuel economy by up to 25% through "power conditioning of the vehicle's electrical systems", but "Consumer Reports" detected no difference in economy or power in tests on ten separate vehicles, finding that the device did nothing but light up. "Car and Driver" magazine found that the device contains nothing but "a simple circuit board for the LED lights", and disassembly and circuit analysis reached the same conclusion. The maker disputed claims that the device has no effect, and proposed changes to the "Consumer Reports" testing procedure, which when implemented made no difference to the results.