How to measure stored procedure execution time?

DECLARE @i int = 0, @TestLimit int = 10

DECLARE @Timing TABLE ( Timing int) 

WHILE (@i < @TestLimit)

BEGIN

      DECLARE @RC int, @ManagerID int =1

      DBCC DROPCLEANBUFFERS

      DECLARE @Start datetime = getdate()

      EXECUTE @RC = [AdventureWorks2008].[dbo].[uspGetManagerEmployees] @ManagerID

            INSERT @Timing

      SELECT ExecutionMsec = datediff (millisecond, @Start, getdate())

      SET @i=@i+1

END

SELECT ExecutionMsec = avg(Timing) FROM @Timing

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