Do you have a smart telephone or tablet? There is a very good app for tuning zitheroos and other chromatic instruments: CLEARTUNE. Easy to read display, costs 3 euros. Find it in your app store or click here for iphone/ipad or android.
Want help with tuning or replacing a string on your zitheroo? I would be glad to help, free of charge, if you send the instrument to me and 10 euros to cover return postage. Call or send an E-mail to let me know before sending the instrument.