Looking for a way to get alerts when users change printer cartridges. Here's the scenario: I monitor toner levels of HP Color LaserJet printers at remote locations. The SNMP Printer Library in PRTG provides me with channels for toner levels of each color, plus alerts when level go below a certain threshold. Now, my primary interest are not the actual toner levels, (because end users replace cartridges themselves as necessary), but the fact that a toner was replaced (leading to a purchase order for new consumables). How can I get a notification based on changes of values within a library channel, and within a certain time span? I.e. getting notified when the toner level of a cartridge jumps up by +70% within 24 hrs. This indicates that the toner was replaced and new consumables need to be ordered. Can this be achieved with library channels at all or do I have to create a custom SNMP lookup first and then build advanced rules on top of that?