Format for DLL calls

My applications are DLLs intended primarily to be called from Excel/VBA, and so my entry points look like:

Subroutine WaterSatDensity_F(TempC, Value, Units)

!DEC$ ATTRIBUTES DLLEXPORT, STDCALL, ALIAS:'WaterSatDensity_F' :: WaterSatDensity_F

!DEC$ ATTRIBUTES REFERENCE :: Units

For one group of installs on a server, Excel is not installed, and so I need a simple way to check that the install is correct, my user licensing is operating and the DLL is returning valid results. I want to write a Fortran main program, which will call the DLL using the same entry points as VBA.  What should my calling program look like?  

Thanks,

David