"Active" diagram when worksheet not open

I have written the following code in FPScript to integrate a flow signal to allow volume calibration. The first two marks indicate a segment of the file with no flow, in order to remove any offset in the signal, and then three “pumps” with a calibrated syringe are integrated, and the results returned. The problem I have is that if the WorkSheet is not open, there is no “Active” diagram, so “Marks=WorkSheet.WKS.MarksIndexX(0)” returns an empty set. This occurs even if the proper folder is active.

Any suggestions?

Thanks,

Paul Warshawsky

Dim Marks,Offset,V1,V2,V3,V4,V5,V6
Marks=WorkSheet.WKS.MarksIndexX(0)
Marks=Sort(Marks,SORT_X)
Offset=Average(c04[Marks[0],Marks[1]])
V1=(Integral(c04[Marks[1],Marks[2]]-Offset))[Marks[2]-Marks[1]]
V2=(Integral(c04[Marks[2],Marks[3]]-Offset))[Marks[3]-Marks[2]]
V3=(Integral(c04[Marks[3],Marks[4]]-Offset))[Marks[4]-Marks[3]]
V4=(Integral(c04[Marks[4],Marks[5]]-Offset))[Marks[5]-Marks[4]]

V5=(Integral(c04[Marks[5],Marks[6]]-Offset))[Marks[6]-Marks[5]]

V6=(Integral(c04[Marks[6],Marks[7]]-Offset))[Marks[7]-Marks[6]]
Return({3/((V1+V3+V5-V2-V4-V6)/6), V1, V3, V5, V2, V4, V6})