custom message for operator

I am looking for a way to give a custom message to the operator on the screen. A simple way to tell him like what operation is going on. Or after probing which dimension is out of tolerance. I know using ASCII file I can do that. But I want to just use my .H file. Message is continuously displayed on the screen until next message is displayed. TNC640
Similar to Siemens MSG("PLEASE TIGHTEN THE SCREWS");