Another natural option is the recursive one:
DECLARE @Example
TABLE (
ID INTEGER PRIMARY KEY,
Inv INTEGER NOT NULL,
Est DECIMAL(9,1) NOT NULL,
Diff DECIMAL(10,1) NOT NULL
);
INSERT @Example
(ID, Inv, Est, Diff)
VALUES (1, 1690, 182, 1508),
(2, 1690, 52, 1638),
(3, 1690, 408, 1282),
(4, 1690, 265.2, 1424.8),
(5, 1690, 600, 1090),
(6, 1690, 18, 1672),
(7, 1690, 18, 1672),
(8, 1690, 92, 1598),
(9, 1690, 4.8, 1685.2),
(10, 1690, 50, 1640);
WITH R
AS (
SELECT E.ID,
E.Est,
E.Inv - E.Est AS Diff
FROM @Example AS E
WHERE E.ID = 1
UNION ALL
SELECT E.ID,
E.Est,
CONVERT(DECIMAL(12, 1), R.Diff - E.Est)
FROM R
JOIN @Example E
ON E.ID = R.ID + 1
)
UPDATE E
SET Diff = R.Diff
FROM R
JOIN @Example E
ON E.ID = R.ID;