Explanation

Box 1: 5 minutes
The alert must calculate the average once every minute.
Note: We [Microsoft] recommend choosing an Aggregationgranularity (Period) that is larger than the Frequency of evaluation, to reduce the likelihood of missing the first evaluation of added time series Box 2: Static Box 3: Greater than Example, say you have an App Service plan for your website. Youwant to monitor CPU usage on multiple instances running your web site/app. You can do that using a metric alert rule as follows:
* Target resource: myAppServicePlan
* Metric: Percentage CPU
* Condition Type: Static
* Dimensions
* Instance = InstanceName1, InstanceName2
* Time Aggregation: Average
* Period: Over the last 5 mins
* Frequency: 1 min
* Operator: GreaterThan
* Threshold: 70
* Like before, this rule monitors if the average CPU usage for the last 5 minutes exceeds 70%.
* Aggregation granularity
Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/alerts-metric-overview