If I'm understanding your post, I see that your Calculator widget in Notification Center on your MacBook Pro always defaults to display -400. You're able to use the widget to enter new calculations, however if you close Notification Center and go back in, it will go back to displaying -400. I'm happy to help!
First, I would recommend removing the Calculator widget from the Notification Center. You can get instructions on how to do that here: macOS Sierra: Use Notification Center. After the widget is removed, restart your Mac by selecting the Apple menu and choosing "Restart..." from the drop down.
After the computer is back on, add the Calculator widget back to Notification Center, and see if it continues to display -400. If so, the next step I would recommend is to boot into safe mode, and test there. More information safe mode, including how it can be helpful and how to boot to it, can be found here: Use safe mode to isolate issues with your Mac - Apple Support.
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notification center calculator widget bug
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