Is event listener required?

I am relatively new to Flash8, have no prior programming experience and this is my first plunge. Performance is inconsistant when using the following conditional statement to direct a movie clip instance to the appropriate frame label:

lowerback_mc.onRollOver = function (){
if (speedo_mc.needle_mc._rotation == -45) {
} else if (speedo_mc.needle_mc._rotation == -90) {

My guess is that an event listener needs to be implemented in order to track the current needle_mc rotation. If so, how? If not, any suggestions?