Sometimes things don't go quite as expected. Connections get broken, switches die, machines crash. Aside from taking reasonable steps to prevent these occurrences, it is especially important in HMIs to be able to gauge the health and accuracy, also called quality, of what is displayed at a glance. For these reasons, components will get visual overlays for various reasons to indicate that the data they are displaying is not good.

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[00:00] Tags have quality built into them automatically. And that quality is reflected on the component on the screen through an overlay system. That way we'll know if we can trust the value that's represented on the screen. So if I look at any tag in ignition, if I expand the tag, if I go down, you'll see a metaproperty called quality, and right now the quality of my tags is good. So that way, on the screen there's no overlay, I'm showing the correct values, so essentially we can trust those values. If we lose communication to the PLC or something happens, that quality will no longer be good. In this case, now it's not connected. You see all my components here got an overlay letting me know we can't trust the value of those tags. That overlay is very important because if an operator didn't see that, they would think that everything communications are okay, and they could be looking at the wrong value. As soon as the communication comes back up for those particular tags, the overlay will go away and we'll start seeing the values coming in again. So the operator knows at that point they can start trusting the values. So here in a second, I'll see my quality come back. There it is, all the tags, all the overlays went away. Now, it is possible on a per component basis to actually remove the overlay binding if you didn't want that. So if I go into the tank here for example and scroll down to the value property, and click on the binding, the very bottom there's an overlay opt out that you can check. So if I check that, the operator will no longer see any overlay on that component. So in this case, if I lose communication again, you see all the other components have got an overlay except for the tank here, and so be cautious if you use that setting, because it can be dangerous in certain situations. You want to make sure you give an indication on whether or not they can trust the values they see on the screen.

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