It depends on the actual resistor values you are using. When the pole goes between positions it may be not connected, or it may make the connection before breaking. If the pole does float then the Analogue input will be undefined. You need to pull that input either up or down with a resistor and then recalculate the values you will get from the resistor network. You can then use a comparator to detect the high or low pulse, assuming that a high or low value will be outside the range given by your resistor network.