Pass Value from Details to Group Footer

I have a formula in the details section of a report. I want to use that value in the group footer. It is blank when I use it. I have tried adding "WhilePrintingRecords" to no avail. My Formula in the Details section is below.

If {ILLM_DRT.DOWN_CODE}= "AS" then

(numbervar a:= datediff( 's', {HIST_ILLUM_RT.SETUP_TIME},{ILLM_DRT.DWN_END_TIME});

numbervar h; numbervar m; numbervar s; numbervar ms;

h:= truncate(a/ 3600);

m:= truncate((( a/ 3600) - h) * 60);

s:= (((( a/3600) - h) *60) - m) * 60; ms:= m +(s/100); ms/60) else 0

My report is setup as GH1, GH2, Details, GF2, GF1.

Any suggestions on how to pass the value to GF2?