Speedo cluster question

Hi guys since I have had the R the speedo is very inaccurate giving underand over readings ( +\- 20mph at speed and has been converted to mph ) also the temp gauge only moves off the needle at 82c and and never gets near its normal area of operation . I have checked both these issues against the read out on the FC commander unit .

Everything else works fine on the unit.
Is it anything anyone has heard of or shall I just get a new unit and see what happens.
Cheers

Do you have aftermarket dials?

As above or just age related lots of clocks are messed up or been interfeared with

First thing I'd do is temporary disconnect the mph converter and see if the speedo is Ok without it. I'd always blame aftermarket stuff first.. Has it got white dials? Often damaged when these are put on.