To try and answer your specific question as to why xlCalculationManual needs to be substituted with -4135, the reason is as follows:
The dynamic link library (DLL) that allows the use of the descriptor rather than the value is not available in Blue Prism. If you ever come across anything else of this mature that you need to devise a code stage for, you can open Excel and go into the Visual Basic Editor (Alt+F11 is a handy shortcut for doing this). In the VB editor you can access the Object Browser in the View menu ( or by pressing F2).
In here there is a search functionality where you can enter the specific descriptor you want to look up, e.g. xlCalculationManual, and it will tell you what the numerical value equivalent is. I have written quite a few code stages by looking up in this way previously.
Hope this helps further.
Paul
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Paul Humphreys
Senior Technical Specialist
Europe/London
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