My speedometer has stopped working?

Anyone know how to fix it. Am I right in thinking that a cable revolves and is connected to the gear box [transmission]?
Update: It's a Fiat Seicento Sporting.
Update 2: Thanks for all your advice. To give a fuller explanation. The speedometer stops and starts. Sometimes it works, other times it doesn't. I'm not sure if it's a cable driven or sensor driven speedometer. When the needle remains stopped the mileometer doesn't count either. So, it appears as if... show more Thanks for all your advice. To give a fuller explanation. The speedometer stops and starts. Sometimes it works, other times it doesn't. I'm not sure if it's a cable driven or sensor driven speedometer. When the needle remains stopped the mileometer doesn't count either. So, it appears as if something is loose or not fitting properly. Also, when it does work the speed it registers is always higher than the speed on my sat nav.
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