Crystal reports running total with stringvar or 2 copies on single page

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VB

CrystalReports

grouping

Hi
I want to display 2 Copies of same report in single page. the problem is (in details section it could be multiple records and I am using group to categorize my data).

What I have tried:

I created a formula and added this in report footer section.

WhileReadingRecords;
Global stringvar letters;
letters := letters + {HMIS_viewTestDetail.testName} + ', '

This work fine for first group. In the next group it is not resetting the data.
for example my view has the following data

ID, depId, depName, testName
1, 1, XRAY, Bone x-ray
2, 1 XRAY, Muscle x-ray
3, 2, Ultrasound, Abdominal Ultrasound
4, 2, Utrasound, Carotid Ultrasound

In the first group my formula is displaying "Bone x-ray, Muscle x-ray" which is ok and next group it is displaying "Bone x-ray, Muscle x-ray, Abdominal Ultrasound, Carotid Ultrasound" instead of "Abdominal Ultrasound, Carotid Ultrasound"

Any help will be appreciated.... Thanks in Advance...