This is a small and strange issue but I'm sure someone will have the solution. I have systems at home and at work both operating Apple OS X Yosemite (Version 10.10.2), and I use the default Calculator widget within Notification Center hundreds of times a day. When using the work system I can access Notification Center and begin typing numbers (via the keyboard) immediately and without problem. When using the home system, however, when I access Notification Center and try to type numbers (via the keyboard) I'm instantly prompted by an alert sound (indicating that the system doesn't know what to do with the keystrokes) and no digits appear within the Calculator widget. As mentioned above; it's a small issue, however I use the Calculator widget so often that my workflow is significantly disrupted when using the home system. Does anyone know how to solve this?