Confusion about nudging documentation

I have found an explanation on fdda namelist in the link :
http://www2.mmm.ucar.edu/wrf/users/wrfv3.1/How_to_run_grid_fdda.html

I don't understand when it is said "If both zfac and if_no_pbl_nudging_uv are turned on, nudging will be set to zero through at least the lowest 10 vertical layers, and higher if the PBL height is larger than the height of the 10th model layer above the surface."

1- Could anyone help clarify the meaning of this?
2- If I want to disable nudging uv below pbl without specifying level in zfac (as I don't know which vertical level is the correct pbl level), what should be the setting on the namelist?

Hi,

I moved this question to it's own inquiry, as it wasn't related to the topic to which it was posted.

1. In the document you reference, the namelist settings are

By setting "if_zfac_uv = 1" (1=on), it means that you are asking nudging to be limited only to the levels above the number of layers set in "k_zfac_uv" (which is set to 10). And then by setting "if_no_pbl_nudging_uv = 1" (1=on), then there will be no nudging taking place through the PBL, which if the PBL height is larger is higher up than the 10th layer, it will extend the no-nudging rule to the top of the PBL, regardless of the setting of 10 for "k_zfac_uv."
2. I think the explanation in "1" above probably answers your question.