SkipVought,
I was able to get it to work using your code. Thank you.
SELECT tblMutualAid.DispatchDate, tblMutualAid.FirstDispatchTime, tblMutualAid.CallNum, tblMutualAid.Unit, tblMutualAid.OnSceneTime, [FirstDispatchTime]+IIf([FirstDispatchTime]-[OnSceneTime]>0,-1,0)-[OnSceneTime] AS [Mutual...