Crystal Reports Sort data by highest %

Message

     Hello,

Can anyone help me please?

I have a very simple report, and I need to sort it descending by a 
%formula I have created.

I only have 1 group and 4 fields in the report (2 of the fields are formulas):

formulas:

@target: 
IF {TABLE.PRODUCTCODE} = "example1" THEN 200 ELSE
IF {TABLE.PRODUCTCODE} = "example2" THEN 150 ELSE
IF     etc............

@%oftarget:
IF Sum ({TABLE.QTY}, {TABLE.PRODUCTCODE})=0 THEN "0.00%" ELSE
(Sum ({TABLE.QTY}, {TABLE.PRODUCTCODE})/{@target})*100 & "%"

my report is:

Grouped by PRODUCT CODE,

then QUANTITY summarized by PRODUCT CODE group

Drop my formulas in, and it returns results like this:

GROUP1      @TARGET       QTY(sum)         % of Target
example 1        200                 100                     50%
example 2        150                 165                   110%
example 3        300                   30                     10%

When I look in the group sort expert, or the reord sort expert, It does NOT show my %oftarget formula so I can sort it descending.

Can anyone advise on what I am doing wrong? or how to achieve it?

Regards,

Mike