dBA Meter app well calibrated with professional noise meter tool OKTAVA 110A-PRO. Measure sound level/noise: -Current average level -Peak level -Average maximum level -Absolute maximum level Graph histogram for (change in settings): -Current average level -Peak level Additional features: -Save measurements -Upside down orientation to easy use. To reset maximum or average maximum - just tap on it. You can self calibrate it in settings (range from -20.0dB to +20.0dB) h381b
improved contrast of readings
Sleep Sounds: relaxing sounds 
Ruler - tape measure length 
Rain Sounds - sleep and relaxation sounds