Update analyze-usage.md

Author: guywi-ms

articles/azure-monitor/logs/analyze-usage.md

@@ -70,7 +70,7 @@ Usage
 | where TimeGenerated > ago(32d)
 | where StartTime >= startofday(ago(31d)) and EndTime < startofday(now())
 | where IsBillable == true
-| summarize BillableDataGB = sum(Quantity) / 1024. by bin(StartTime, 1d), DataType 
+| summarize BillableDataGB = sum(Quantity) / 1000. by bin(StartTime, 1d), DataType 
 | render columnchart
 ```