Speedo - milometer intermittantly working

[boner]

Recently, my speedo milometer stops working for a few miles, sometimes more. Then starts to click every 10th mile(which is correct,) but every time it clicks it incriments the mileage by 1 mile. then after a while it reverts back to normal operation, 10 clicks = 1 mile. is the speedo at fault or an elec fault.. Thanks