I own a 1993 Dodge Stealth ES. I have a feeling my speedometer needs to be re-calibrated because the needle sits below the 0 when at idle. I don't know much about it, but that doesn't seem right. I know my speedometer reads 10 mph slower than what i am actually going because ive been on roads where cops have electronic speed sensors setup to track your speed. Would this be the cause? If so, how can I go about fixing it?

Here is a pic of my current speedometer:
http://i41.tinypic.com/33tqrm9.jpg