Just fit it, power on, rotate filter to get desired filtering.
I never look at the numbers on the filter apart from first fitting one as in bright day use this one dull day use this one.
I talked to Freewell support but they didn't help me so I write this here.
There is no instruction in the box or in the site so I don't know which number symbolize what. Thanks for helping.
logo = ?
2,3,4,5 = ?
6,7,8,9 = ?
This video may help with the settings. There are others. Also note that with the variable you can set it in between the standard individual settings... like dial in for ND24 equivalent by rotating midway between 16 and 32 settings.