calculation values

Hi all,
I had posted a problem,and I didn't get the obvious solution, can you help me please:

My table looks like the following:

Date\Time Counter1 Counter2

The counters are taken by an automatic system in three shifts:
First in : 6:00 AM Second in: 15:00 PM Third in : 11:00 PM

I want a query to calculate the difference of the counters between the three shifts (Let's begin with this).

For example: The following table
22/11/04 11:00 PM 0 0
23/11/04 6:00 AM 10 20
23/11/04 15:00 PM 20 30
23/11/04 23:00 PM 30 40

The output is:
23/11/04 6:00 AM 10 20
23/11/04 15:00 PM 10 10
23/11/04 11:00 PM 10 10

I'm new I the SQL world. can you please help me and give me sum information to solve the problem.the answer is here -- http://www.dbforums.com/t1063139.html|||But, the answer isn't sufficient to my problem.
thanks...|||then you will have to ask your question a bit more clearly

maybe we do not understand the problem|||I'll explain secondly,
my really table is the following:
1. CollectDate (Date/Time): The date and time of collecting data.
2. MachineNum (Number): The machine number of the data. I have 40...50 machines.
3. WorkOrder (Number): A number witch discribe the part of the machine.
4. TotalGood (Number): An accumulator of the current parts that the machine did.

The total task of the query is to calculate how many parts did the machine do in a certain date but by shifts.
E.g:
the final date collection was:
CollectDate MachineNum WorkOrder TotalGood
25/11/04 23:00:00 40 00111 100
26/11/04 6:00:00 40 00111 200
26/11/04 15:00:00 40 00111 500
26/11/04 23:00:00 40 00111 1000

The query output is:
Shifts(26/11/04) MachineNum WorkOrder TotalGood
6:00:00 40 0011 100 (200-100)
15:00:00 40 0011 300 (500-200)
23:00:00 40 0011 500 (1000-500)

Please help me.
Best regards...