This system receives it's information from two sensors, one fitted to the steering wheel and one to the rear tyres. This enables the steering wheel position to remain constant in relation to the angle of the rear tyres so that the forklift operator knows exactly what the angle of the rear steering wheels is.
Although it is possible to get a good idea of rear wheel angle by looking at the steering wheel on most trucks, this system makes it far more accurate.
Having driven hundreds of forklift trucks over the years including those fitted with SAS I firmly believe that Toyota's system of active stability is the biggest step any manufacturer has made towards the safety of forklift trucks. The only machine that comes close in this respect is the Still R70. Of course, if you know different please let me know. Toyota SAS System