title: Excel: why the value of a blank cell is zero?
body: <p>Suppose there is an empty excel sheet. Enter formula "=A1" into the B1 cell. The value of B1 would be 0.</p>
  
  <p>My question is: why the value of B1 becomes zero when referring to an empty cell A1? Any rationales Excel behaves this way?</p>
  
  <p>Thanks.</p>