A severity of a particular type is trigged whenever the returned value from the check is higher than the configured threshold, the baseline.

The notification threshold / baseline can be defined in several ways.

Setting Description
Method  Constant / Average / Median / Deviation
Percentage  Percentage threshold based on the calculated value.
Deviation  Number of standard deviations
Period  Time period for historical results to include in the calculation. 
Offset  Constant to add to the calculated value. 

Static calculations uses a constant threshold value.

Dynamic methods calculate the threshold value on the fly, based on a combination of the type (percentage or deviation), the method (average, median, deviation), the period (time frame for historical data to use), and offset which is added to the calculated value.

Method Calculation Type Example
Constant   A fixed value. Static  25
Average Average. Dynamic 120% of the average returned value for the last 2 hours + offset 50.
Median Median. Dynamic 120% of the median value for the last 2 hours + offset 50.
Deviation  Standard deviation. Dynamic 2 standard deviations + average value for the last 2 hours + offset 50.