title: Display Excel VBA message box when a cell within a range changes AND meets a given criteria
body: <p>I need some help creating the Excel VBA to display a message box when a any input range to a calculated cell (cell with a formula in it) changes and meets a given criterion for the range.</p>
  
  <p>For example, the range "B2" contains calculated cells which are a function of "A2", and if, upon updating the input, "A2", the recalculated cell, "B2" exceeds 20%, I want to warn the user with a message box.</p>