Trouble Joining On Datetime

Hello -

I have a table that looks like this:
Code:ID Station DateTime Value 1 ABQ 10/8/2005 1:00 am 102 ABQ 10/8/2005 2:00 am 203 ABQ 10/8/2005 3:00 am 254 ABQ 10/8/2005 4:00 am 5...
I am trying to build a query that, for each record, gives me the values for the previous 2 hours.

So my goal would be a query that returns:
Code:ID Station DateTime Value ValueT-1 ValueT-21 ABQ 10/8/2005 1:00 am 10 Null Null2 ABQ 10/8/2005 2:00 am 20 10 Null3 ABQ 10/8/2005 3:00 am 25 20 104 ABQ 10/8/2005 4:00 am 5 25 20...

I created a table (NewTable) that, for each record, has the DateTime, DateTimeT-1, and DateTimeT-2. So columns in Newtable are ID, Station, DateTime, Value, DateTimeT-1, DateTimeT-2 where DateTimeT-1 = dateadd("h",-1,DateTime) and DateTimeT-2 = dateadd("h",-2,DateTime).

I then joined (using a left join) this new table to the original table on [NewTable].[DateTimeT-1] = [OldTable].[DateTimeT].
so code is
Code:select [NewTable].ID, [NewTable].Station, [NewTable].DateTime, [NewTable].Value, [OldTable].DateTime, [OldTable].Value AS ValueT-1from NewTable left join ON [NewTable].[DateTimeT-1] = [OldTable].[DateTimeT]

The output does not pull all the right records. Some of the records have Null values for ValueT-1 when the datetimeT-1 is in OldTable. So for some reason the join doesn't seem to be working.

Hopefully this is clear. Any thoughts? Help is very much appreciated!

Thank you!