I've never heard of this, but here is a thought about a possible troubleshooting step.
Do a search for the file
CALC.EXE
*This is the windows calculator and should be found in
C:\WINDOWS\CALC.EXE
Since this is a system file, you will have to allow the search to include hidden system files.
When you find the file, right click on it and rename it to something like:
CALC1.EXE
Then start your Sim City game. You may see an error, like "Can't find C:\WINDOWS\CALC.EXE".
The error message may then give you some clues about what is calling for the CALC.EXE file.
When finished troubleshooting, go back and rename your CALC1.EXE file to
CALC.EXE
If you don't see any error while the Sim City game is running, then I would guess the Calculator open command is coming from somewhere else.
Dwight
*I don't know what version of Windows you're running, so it is possible the Calculator filename may be slightly different. If you can't find the file, right click on the Calculator shortcut in The Programs/Accessory menu and choose "Properties". Then click on "Find Target" and it will open the folder where the calculator executable (.exe) file is located.