actually its really cleaver its made so even a monkey can opperate it. it connects to power and thats it.
its rpm reference signal is the back emf that altinator produces. as the altinator rotates it creates pulses/bursts of energy, Because an altinator generates 3 phase ac current whitch is converted to dc current through a series of diodes. you might not see this signal on a multimeter however on a occyliscope it is quite clear. the shift light has a small processing box which captures this unique signal and uses it as the Rpm signal. kind of like a g-tech (i think thats what the gizzmo is called.) so the answer to your Question is yes it is accurate and yes it is real time but you will need to set it up. as there is no rpm specific setting due to it can be used in anything from a car to a truck. you have a knob to set the lights brightness (and let me say u need the brightness knob because the high intensity blue leds in the shift light are F%$king bright) and another with rpm low/high so an accurate working tacho is required to set it up. They are simple and easy so even the most car illiterate person will find it hard to stuff up the installation. Plug, play, set & Forget its that simple.
I hope that answers yours and anyone elses questions about the shift light.
Kind regards
Dave