This article applies to PRTG Network Monitor 13.1.3 or later

Set Limit Markers in Graphs

PRTG’s graphs will automatically display limits you set in the sensor channel settings. You can set upper/lower error and/or warning limits. Limits will automatically set a sensor into Warning and/or Down status. Each limit will automatically be shown as a yellow or red area in a sensor graph if you configure the graph to show one sensor channel only.

For example, a traffic graph with limits can look like the following:

Click here to zoom

Configuration Step-by-Step

In order to create a graph display like this, please ensure the following:

1. In the sensor channel settings, in the Display section, set the option Hide from graphs for all sensor channels except for one—the one you want to have a graph with limits for.
2. For the remaining sensor channel, in the Limits section, Enable Limits and set error and/or warning limits. Save your settings.
3. Return to the sensor’s Overview tab to check the graph display. In order to get a filled graph, set the remaining sensor channel as Primary channel for this sensor. All other sensor channels will be displayed as a line only.

Other alternative(s):

For "visual markers" only (A limit which doesn't affect the sensor's status) you may employ a Sensor Factory Sensor.