If I create a query for all the records in the db (9481), and request table output and then on the table click on Plot on Chart, I go to the chart page but get a php out-of-error message when creating the array of result objects.
If I create the same query and request a chart output, all is well. If I then ask for table output, all is well. If I switch back to chart, all is well.
I don't get why I get the error in the one case and not the other.

I reverted back to one query and results in half a dozen files (i.e. undid the changes documented a couple of posts ago). I used the //2to1 comment tag at each change and commented out my recent modifications, but left them all in there. That reduced the amount of memory I needed, but not as much as I hoped. So, I added a statement in the config.php file to allocate more memory to the process, and that worked. Given the absolute numbers aren't huge (64MB to 128MB) and relatively modest user-demands, I think this will be OK.