Here is one idea.
Very simple example.
[count Users]/attr([User Registered])
average_incl_Null_SM_9.1.twbx 12.2 KB
There may be Users whose available capacilty
had been not utilized at all in the reported days.
A common approach is to build a "capacity" table
to join (or blend) with a usage one.
Please find the attached (Shin, your wb has been utilized :-)
average_incl_Null_SM_9.1_YF.twbx 92.0 KB