Tachometer fluctuates

My 1992 Hond Accord EX with 2.0 fuel injected has a tachometer problem. At times the tach will jump 10-20 rpm's for no reason. It will jump back and forth back and forth and then it will stop jumping and register correctly. This only happens at speeds between 20-60 mph. The engine runs well and the speedometer is ok. Has anyone experienced this problem and if so I would appreciate your input.

Thank You