TSQL Difference between 2 rows

use AdventureWorks2012;

select

CustomerID,
OrderDate,
TotalDue,
sum(Totaldue) over(partition by CustomerId order by OrderDate Desc ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING ) as LastOrderAmount,
TotalDue - sum(Totaldue) over(partition by CustomerId order by OrderDate Desc ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING ) as ChangeFromLastOrder from sales.SalesOrderHeader

order by CustomerID, OrderDate Desc

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