You can use this app to tune your guitar, bass, and ukulele up to 0.01Hz of sensitivity(in a silent room).  

Just bring the indexes to the center with green area and you are in tune.

Just pay once for the extra features for the lifetime

No subscriptions or auto-renewals

Some of the features are
* more than 50 types of guitar tuning(drop, open, etc)
* 9 types of ukulele tuning (including tenor, soprano, baritone, etc.)
* 8 types of bass tuning
* 6 types of banjo tuning
* 7 types of mandolin tuning
* auto and manual string selection
* both octave and tone approach indexes
* warning for too tight strings which may break(in manual string selection mode)
* phoneAmp amplifier with common studio effects and recording feature
* metronome with grouping of beats