The “Sound Out” mode lets you listen to a reference tone emitted by the internal speaker, allowing you to tune by ear. A reference tone in the range of C4 (261.63 Hz) to C5 (523.25 Hz) can be output. You can check the pitch using both eye and ear, allowing you to tune more accurately, and also providing an ideal method of training your sense of pitch.
The CA-50 can be used for approximately 135 hours (when using zinc-carbon batteries). When the remaining battery capacity runs low, the display shows an indicator, letting you know that it's time to replace the batteries.