Programming iFix

[santiagoplc]

Hi to everyone, I'm new in ifix, and I'm trying to create just a simple graphic so I can start knowing a litle better this software, I've already done all the communication issues with my AB 1756 L71 trough OPC and I've created the database with the tags that I want to work with, but when I try to create a pushbutton that should toggle a bit inside the plc I've found that the expression builder gives me (among a large list of option) two possibilities: A_CV and F_CV, can anyone tell me the differece between this two options? Or even better: can anyone tell me where can I download a description list of all the options that the expression builder is giving me? (so I can study a little bit more and I don't have to do such a basic questions). Thank you all in advance.