Excel: count UNIQUE numeric values in column

PROBLEM

 Count DISTINCT values in Excel column.

SOLUTION 

Copy-paste formula substituting the column range:
=SUM(IF(FREQUENCY(IF(SUBTOTAL(3,OFFSET(A7,ROW(A7:A10000)-ROW(A7),,1)),A7:A10000),A7:A10000),1))

Similar with Excel Table ranges:
=SUM(IF(FREQUENCY(IF(SUBTOTAL(3,OFFSET(Table1[[#Headers],[T_TBL_ID]],ROW(Table1[T_TBL_ID])-ROW(Table1[[#Headers],[T_TBL_ID]]),,1)),Table1[T_TBL_ID]),Table1[T_TBL_ID]),1))

Example:

DETAILS

The formula formatted break down:

=SUM(IF(

        FREQUENCY( 

                  IF( SUBTOTAL(3,

                                  OFFSET(Table1[[#Headers],[T_TBL_ID]],

                                         ROW(Table1[T_TBL_ID])-ROW(Table1[[#Headers],[T_TBL_ID]])

                                         ,,1))

                              ,Table1[T_TBL_ID])

                    ,Table1[T_TBL_ID])

                  ,1)

      )

    )