title: Excel Data Validation B1 cannot be blank if A1 is not blank
body: <p>So A1 is a list, it has ignore blanks enabled because it is not required, and the values are derived from a defined name range. the source is <code>=procedureType</code></p>
  
  <p>B1 is a list that is derived from the value in A1. The source is <code>=CHOOSE(MATCH(A1,procedureType,0),consultType,diagnosticType,interventionalType,screeningType,therapeuticType,treatmentType)</code>. This works as intended. It is currently set to ignore blanks.</p>
  
  <p>However, I would like to make B1 a required field IF A1 has a value in it. How do I conditionally do this? B1 is not required if A1 is blank, and it is required if A1 is not blank.</p>
  
  <p>Thanks for your help!</p>