>>Do you want to group by each hour? If so, GROUP BY LEFT(dType, 13).
>>
>>If you want to group by date only, GROUP BY LEFT(dType,10)
>
>At this point I want to GROUP BY each 10 seconds, i.e. 1/6th of a minute.
>I'm sure that at some point I will want to consolidate larger chunks of data. Thanks for the help.

That's tricky, especially in VFP (much easier in SQL Server).

Ok, try

SELECT max(cast (Dtyme as datetime)) AS DateTyme, AVG(DCreading) AS DCreading, ;
	SPACE(10) AS cDate, SPACE(8) AS cHourMin ;
FROM CPdata  WHERE RType=[DC] ;
	GROUP BY ROUND ((cast(dTyme as Datetime) - datetime(1900,1,1,0,0))/10,0) ;
 ORDER BY LEFT(Dtyme,10) ;
	INTO CURSOR CPchart  READWRITE
&& round to 10 seconds.