Reset button has 2 functions:
1) If the button is held for 3 seconds during normal operation, it will
cause a reboot of the device.
2) If the button is still held after reboot (during power-up), it will cause
a factory reset.
There are 2 types of factory reset procedures, soft reset and hard reset.
1) If the reset button is held for less than 5 seconds after reboot (during power-up), it causes a soft factory reset which resets device settings to default, but leaves the user database and logs intact.
2) If the button is held for longer than 5 seconds after reboot (during power up), it causes a hard factory reset, effectively wiping the entire device memory, resulting in out-of-the-box state.