At the Digitrax Site: http://www.digitrax.com./mobdec.htm#dn149k2 They have a paragraph: Digitrax REAL FX features: Light Up Your Life and MORE! Don't settle for less than Digitrax Real FX features! Digitrax Real FX is more than just flashing lights Digitrax uses sophisticated algorithms to simulate truly prototypical lighting in your locomotives. With Digitrax Real FX you will think you are looking at the real thing! Digitrax Real FX decoders incorporate 4 user configurable & independent special effects generators for prototypical special lighting effects. Set up a Mars light with just one lead. Use three Real FX functions to make your ditch lights be on when the engine is running and then flash alternately when you approach a grade crossing. Use two Real FX functions to put realistic firebox flicker in your steam locos! Gyra lights, single and double pulse strobes, strato lights (rotating beacon), Rule 17 dimming are also available. I am not familar with Rule 17 dimming???