@Gillslady: That's strange. Have you tried checking your Recent Apps to see if it's open in the background, and closing it to see if this helps? If this isn't applicable, swipe up from your Home Screen > Press and hold on the Calculator app icon > App Info > Storage > Clear Cache > Clear Data, then press the Volume Down and Power Keys together for around 10 seconds until the phone restarts. If the issue persists, although not ideal, you can also press and hold on the Calculator app icon > Uninstall.
