Wanted Tiny Tach or similar

[jangiolini]

Hi folks any of you nice people out there have a tiny tach or some other low cost digital tacho for sale?
I have reason to believe that my tacho on my 582 is reading a little low! and I am looking to double check it. I have an optical tacho left over from my model flying days and will try it but still would like to install a digital one.
Thanks
John.