Need to compare your readings from one sensor to a baseline or background data from another? A Reference allows you to create variable or reference points from parameters monitored by 1 or more device using statistical functions over a given time period.

From the Alerts editing page, select References and then choose the Function, Node(s) and Time Period as applicable.  Once you've setup a Reference, it'll be assigned a sequential letter name, i.e. "A" for the first one.

Then in Conditions, choose the letter name of the Reference you just created as the Node, and select the comparator and value as normal.

In the above example, we can use the Difference function to set up an alert for when it's dustier at Station 1 then the Baseline. We select the Station 1 node first and the Baseline node second because the function simply subtracts (node 1 - node 2). When Station 1 exceeds the Baseline we get a positive number. We then complete the condition as A > 0.125.

Think of the equation as:

Minimum (MIN): Returns the minimum value over the rolling time period.
​Maximum (MAX): Returns the maximum value over the rolling time period.
​Average (AVG): Returns the average over the rolling time period (moving average).
​Difference (DIFF): Returns the difference between node 1 and node 2.
​Absolute Value (ABS): Returns the absolute value of a reference

Choose a time periods between 5 minutes and 1 month for the Min, Max and Average functions. The available intervals are:

These functions are similar to the Statistics you can add when configuring your device.