I am trying to work out how to get percentage of 'Appointment' to calls when Summarising by a week. I can do this per day by using a custom formula by in the Summary View I can only group data by SUM or AVG which does not give me the correct value.

Table Fields

Date, Calls, Appointments 

Percentage of 'Appointment' to 'Calls' formula

Appointments / Calls

Example

05 Jan 2012, 20, 8  (40% 'Appointment' to 'Calls')

06 Jan 2012, 10, 7  (70% 'Appointment' to 'Calls')

Total 30 Calls, 15 Appointments
The correct percentage is 50% but base on SUM I get 110% and AVG I get 55%

Is there any way using the summary view that I can get the correct percentage over a period of time.