SELECT 
Tabe.IDMezzo, 
Tabe.KmRif, 
Tabe.KmRif-Nz((SELECT Max(T.KmRif) FROM Tabe AS T WHERE ((T.IDMezzo = Tabe.IDMezzo) AND (T.KmRif < Tabe.KmRif))),0) AS Diff
FROM 
Tabe
;