Focus 1.6 16v on a 51 plate (2002)

When changing gear up or down the rev counter jumps, eg. if i change up a gear whilst doing 2000rpm, the rev counter jumps up and hits 3000rpm and vice versa for changing down the box.

I have also noticed, that if i depress the clutch whilst driving the rev counter shoots up before dropping down to around the normal 800 rpm.

Also which sensor sends the revs signal thru to the rev counter.

STUMPED!!!!!

Any ideas????