The Pro Tuner (available in the Tune Player Pack, or individually for $0.99) will allow for non-standard tuning references from A=420Hz to A=460Hz.
- Open the Pro Tuner
- Tap on the settings icon in the upper right corner
- Scroll down to 'Reference Pitch' and tap on the pitch to open the Reference Pitch settings
- Use the scrolling wheel to choose a reference pitch and then return to Tune Settings and tap Done in the upper right corner