Rules in the sense.Did not get your question..See 
correlation comes into picture for dynamic values which are 
returned from the server.. Common Dynamic values being 
Session Id, Account number which is generated on filling a 
bank account opening form, Transaction Id etc..

Thank u Mr Naga,

        suppose i am testing a telecom domine project,so 
how can i find the correlated values,

          as my knowledge correlated value is nothing but a 
uniq key elements right(witch is not duplicate)

Correlation means capturing a dynamic value which is 
generated from the server. you can clearly know these 
values by seeing your script as they looks like a strange 
values. After running the script in the extended log,You 
can search the name of the value in the execution log and 
find out the left and right boundary and include the 
web_reg_save_param function in your script before the 
dynamic value and then parameterize the dynamic value in 
your script by deleting the dynamic value and give a name 
enclosed in clurly braces to the dynamic value. Then run 
your script. your script should pass if you mention correct 
right and left boundaries.

To answer Naga first, i think what he wrote <may not be 
meaning> about is Auto Correlation rules that are found in 
Recording options at the last tab
<In case if it is being misunderstood; just to avoid 
exploration in wrong direction>.

Assuming it to be normal correlation of dynamic values 
sought by server, for session authentication and validation.

Here what you can try is, after recording, check for 
recording / replay log<detailed>, where you can search 
common data chunks between certain response and subsequent 
request. IF there is something common, it means that value 
which was returned in the respnse was expected ny the 
server in consequent request.
>> Inferrence this peice was candidate for correlation.

I believe Correlation is a hot and very important topic in 
Load Runner which is asked in every Performance Testing 
interview.

Srinivas I did not undertand what you are trying to anser 
me. I have quoted the examples based on the work I do. 
Generally we correlate the account number, trasaction id as 
I am from a Banking Domain. Chandana wherther you are 
working on a Telecom or from any background..it doesnt 
matter Correlation is used for any dynamic data which is 
sent from server.

Automatic correalation is not useful always there are some 
dynamic values which automatic correlation can detect. For 
this reason it is preferred to go with manual correlation 
which Rani has explained.

For a better understanding you can check the following link 
which has a very good explaination about correlation:

http://motevich.blogspot.com/2007/10/loadrunner-scripts-
correlation-tutorial.html

if u wnat find Correlation values just record the script 
twice and compare them from comparision u came to know what 
are the dynamic values in ur script.other wise u can use 
beyond compare s/w u can compare bothe of the scripts.

if u use .net(my application) based application these type 
of dynamic values u will get
28.	VsKey Correlation Path	: web_reg_save_param
("vskey1","LB=__vsKey\" value=\"","RB=\"",LAST);  
29.	ViewState Correlation 	: web_reg_save_param
("viewstate1","LB=__VIEWSTATE\" value=\"","RB=\"",Last);
30.	Event Validation Path	: web_reg_save_param
("evehan1","LB=__EVENTVALIDATION\" value=\"","RB=\"",LAST);
31.	Control ID path		: web_reg_save_param
("ControlId","LB=ControlID=","RB=&",LAST);
32.	Report Session ID 		: web_reg_save_param
("ReportSessionId","LB=ReportSession=","RB=&",LAST);
33.	Session ID Path		: web_reg_save_param
("SessionId","LB=Search in general log","RB=Search in 
general log",LAST);

Hi chandana 

correlation is very simple, it means to capture the dynamic
values which are sent from the server. rules in the sense,
this procedure we hve to follow for doing correlation in a
simple manner.

stepl:- generate the two scripts for the same actions;

2) then you hve to compare the two scripts by using wdiff
tool, it is a part of vugen component. 

3)identify the dynamic values which are different from each
other like transaction id's and session id's etc.

4)copy the value which you would like to correlate and find
out in the script and go to tree view, check the value in
the server response. ctrl+f

5)by using this function
web_reg_save_param("parameter_name","LB='some
value'","RB='some value'","ord='number'","Last");

6)Enable the extended logs in the runtime settings(VUGen)
and click the parameter substitution.

7) compile and run...

8) check the values in the output window wheather it is
sucessfully or not. the line will be appeared in blue colour.