The EHX-2020 can be calibrated to a reference standard of 436 to 445Hz in 1 Hz steps so being able to tune to and play together with instruments that might not be at 440Hz is not a problem.  It has a wide tuning range of B0-B7, plus three flat tuning modes so you can tune down ½ step, a whole step or a minor third.  When the tuner is engaged your output is muted.

Electro-Harmonix EHX - 2020 Chromatic Tuner Pedal

$53.99Price
  • -Chromatic pedal tuner with a tuning range of B0 to B7
    - True bypass allows your input sound to be output with no change or coloration
    - The pedal’s output is muted when the tuner is engaged which makes it ideal for live performance
    - Accuracy: +/- 1cent
    - Calibration: 436-445Hz (1 Hz steps)
    - Three flat tuning modes
    - 9V power supply included