RDA - Top SQL report

Hi,  

The question is regarding (Remote Diagnostics Assistant; Metalink Note: 314422.1) Oracle Support provides to troubleshoot performance issues in a database {RDA} and the calculation of the "Top SQL Report"  

More specifically, I am curious how the following ratios are deemed "Expected Respose Time (in Seconds)"  

From v$sqlarea:
{ (disk_reads/executions)/50 }
{ (buffer_gets/executions)/500 }
 

Also, what is the significance of the numbers 50 and 500 respectively?  

Queries used in the report:  

select
 sql_text,
 executions,
 disk_reads / decode(executions,0,1, executions) / 50 from
 v$sqlarea
where
 disk_reads / decode(executions,0,1, executions) / 50 > 100 order by executions desc;

select
 sql_text,
 executions,
 buffer_gets / decode(executions,0,1, executions) / 500 from
 v$sqlarea
where
 buffer_gets/ decode(executions,0,1, executions) / 500 > 100 order by executions desc;  

Thanks,
Sri    

--
http://www.freelists.org/webpage/oracle-l