Speedometer reading problem

[Ehlolzau]

G'day all,

I have a 2000 Hyundai accent and today while driving i noticed it had a speedo reading error.

I was sitting on a hill and it was raining and i let out the clutch and the wheels spun trying to get traction,( front wheel drive) after this i noticed i had a speedo reading error. When i am sitting at a light and i take off the speedo will go from 0-60 with just a push on the gas peddle. It reads but the speed it is reading is incorrect by a long shot. What should i be looking at first?

All other readings are fine, revs etc. its only the speed reading.

any help would be must appreciated.