Missing Grand Total for a Calculated Field in a Pivot Table
 

I created a calculated field called "rate" that is equal to "Field1/Field2"
in a pivot table. The calculation displays the correct quotient in the
sub-total and individual grand total fields. However, the overall Grand
Total is always 0%. Below is an example of the problem

Group Category Jan. Feb. Mar. Grand Total
North Field1 10 15 20 35
Field2 5 10 15 30
Rate 2.0 1.5 1.3 1.67

South Field1 15 20 30 65
Field2 5 10 15 30
Rate 3.0 2.0 2.0 1.85

Grand Total (rate) 2.5 1.75 1.67 0

Can someone tell me what is going on? What can I do to replace the "0" with
the correct calculation?