Explanation
Azure Monitor autoscaling allows you to scale the number of running instances up or down, based on telemetry data (metrics). Scale-in occurs when the instances are decrease. For this rule the instances are decreased when the CPU usage is 60% or lower.
References:
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/autoscale-custom-metric
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/autoscale-common-metrics