When Excel formulas don't work

Today one of my colleague asked me why formulas in an Excel worksheet did not work, as shown below,
Somehow I remember there is a SHIFT+F9 to rescue even though I don't know why. After half of an hour of Googling I realized it was because automatic calculation was disabled. To make it worse, the automatic calculation settings are carried from original Excel workbook when you copy its content into a new one.