How to check the value of a field within the current node? In order to display a block only above certain nodes of Article content type, 
I created a boolean field with two values : On / Off

The goal is to display the block only above the articles that have the Off value 

After enabling the PHP filter module, the block gives me this option : "Pages on which this PHP code returns TRUE (experts only)" but i haven't been able to figure out the php code that returns TRUE

( Can the context module achieve this without PHP ? )

Any help is help
I think you should be able to do this with the (https://www.drupal.org/project/rules_block_visibility) module.