Since you haven't posted your query, I've got no idea why Access keeps
changing it.  Nor do I see why it would need to - it does that only when you
enter something in the SQL which it cannot display in the query grid, and
there's nothing you need to do that requires that here.

The following query gives the averages for the two date ranges and the
difference in those averages [that's what you ask for with "... those two
calculated values ...", and I presume that's what you mean when you say "...
show Parameter1 from start1->end1 ..." - there will not be a single value of
Parameter 1 across the date range - unless it never changes :-).]

It assumes your table is named tblParameterData; it prompts for the start
and end dates of the two date ranges.  I have named the date field as
MyDate - you should not use Date as a field name; it is a reserved word in
Access.

SELECT Avg(T1.Parameter1) AS AveP1D1, Avg(T1.Parameter2) AS AveP2D1,
Avg(T2.Parameter1) AS AveP1D2, Avg(T2.Parameter2) AS AveP2D2,
Avg(T1.Parameter1) - Avg(T2.Parameter1) AS DiffP1, Avg(T1.Parameter2) -
Avg(T2.Parameter2) AS DiffP2
FROM tblParameterData AS T1, tblParameterData AS T2
WHERE (((T1.MyDate) Between [Start Date 1] And [End Date 1]) AND
((T2.MyDate) Between [Start Date 2] And [End Date 2]));

This query does not - and cannot - return the start and end dates for the
two data ranges.  However, you can include them in a report based on this
query.  To do so, simply add four unbound text boxes to your report, and set
their control sources to the four parameter strings; they must match
exactly, so in this case, the control sources would be:
   =[Start Date 1]
   =[End Date 1]
   =[Start Date 2]
   =[End Date 1]

HTH,

Rob