Help: How to make block procedure activate at certain height.

I have a block that basically acts like a very cheap representation of a drilling rig of sorts, which has a gui you can access to activate it and make it "drill".

The procedure is activated from pressing the button in the gui to turn the drill on. 

But I want it to only be able to activate at a certain height, so players can't just plop it down anywhere they want and drill.

Is there a procedure for blocks that do this?

Something like 

If [ [Get block z] = [30] ]
do > (Rest of Procedure) 

... I see a bunch of variables with blocks, but it's all [Is [block] [z] [x] [y] waterlogged]], or [is [block] [z] [x] [y] farmable]]. 

But there's no [is [block] at [x] [y] [z]]

Am I missing something?