I am trying to hide certain values in a field that has 4 selections in a drop down list based on the value of another field. 
For example:

If abc is 123 and the choices for xyz are 5, 6, 7, 8, I only want to allow 5, 6, or 7 to be available for selection. 

 

The reason I want to do this is there are 3 choices for field abc and depending on that choice sets the allowable choices for xyz.

 

Thanks