14 CFR §27.1321

1. (a)Each flight, navigation, and powerplant instrument for use by any pilot must be easily visible to him.
2. (b)For each multiengine rotorcraft, identical powerplant instruments must be located so as to prevent confusion as to which engine each instrument relates.
3. (c)Instrument panel vibration may not damage, or impair the readability or accuracy of, any instrument.
4. (d)If a visual indicator is provided to indicate malfunction of an instrument, it must be effective under all probable cockpit lighting conditions.