Speedo?

I have a 2002 PX200E. Millenium edition, with 1300km. It has the white faced speedo. We have been having cold weather and when riding a few days ago. I noticed that the speedo was reading 20 mph while not moving at all?!? It also reads about 20 mph faster then I am actually going when riding around. Is this a cold weather problem? Or something that has to be adjusted or replaced?
Thanks
PXR

Thanks for the reply Her Doctor[;)]
I will give what you said a try and let you know what happens.
PXR

sometimes a small piece of shrapnel can get in the way of the needle or spring and stop it returning or going up.easy test is to take the headset top off with the speedo still in it and tap it down against the palm of your hand toward what would be the throttle end a dozen or so times this may dislodge any foreign body.failing that you may well have a faulty speedo but try the cheap option first eh?.hope you sort it,there are too many speed cameras about these days not to have a speedo

stroud valleys(midnight hour)sc est 1984