Make a drop down cell mandatory when certain drop down options are selected.

I have a table with drop downs. Let's call them "Device" and "Method". If someone selects a certain "Device", I want to make the "Method" cell a mandatory entry (drop down as well). Any help would be greatly appreciated. Thanks!

How do you want to make it mandatory? Meaning, lets say the "Device" drop-down is in cell A1 and the "Method" drop-down is in cell K1. If I select a value from the drop-down while in Cell A1, after hitting Enter, what do you want to happen?