Hi Richard,
One of the reasons is I can write high speed programs, that interface directly into MySQL databases....in about five lines of code.
This is the bit that does the differentiation.

 WITH Mytable1 DO
     BEGIN
       tmp1:=0; tmp2:=0;
       first;
       while not EOF do
        BEGIN
         edit;
         Fields[2].Value:=fields[1].Value - tmp1;
         Fields[3].Value:=Fields[2].value - tmp2;
         tmp1:=fields[1].Value;
         tmp2:=Fields[2].Value;
         next;
       END;
     END;
 

That is AUTOMATICALLY passed to the bought-in graphing component that delivered the screenshots above. So the development was:
Drop in database component.
Link table to datasource.
Drop in graph component.
Link datasource to graph.
Add code above.

...took about 20 minutes. I love Delphi.

Steve