How to do correlation in Loadrunner? at what point of time it requires?

correlation is done to instruct load runner not to stop execution of the script when it finds dynamic value.Once correlation is done to the script we dont get any correlation errors.We can do correlation in 2 ways

1.Manual
2.Auto

First go for auto correlation for this after recording the script scan for correlated values the correlation studio in vugen list out all the values that are needed to be correlated then click on correlate all the dynamic values.Then run the script hope the script runs without any corr errors.
If not we have to do manual correlation.

Hi there, i am also new to lr. I found good traingin vedio clips. Below is the demonstration to do manual correlation. There are bunch of video which you can get start with lr. load runner tutorial 9 by javaguru -- revver online video sharing network

Correlation is a statistical measurement of the relationship between two variables. Possible correlations range from +1 to –1. A zero correlation indicates that there is no relationship between the variables. A correlation of –1 indicates a perfect negative correlation, meaning that as one variable goes up, the other goes down. A correlation of +1 indicates a perfect positive correlation, meaning that both variables move in the same direction together.

Correlation is the technique used to handle dynamic values in replay. We specify the Left & Right Boundaries of the Dynamic Values.

Correlation can be done by 3 methods
1. Manual using web_reg_save_param() function
2. Automatic correlation.
3. Correlation Rules.

Normally people gets confuse with Parameter and Correlation.
When we access any web application, Every time server machine sends different session values to client machine for that particular session, and this dynamic session values creates errors, the method to identify and set the dynamic generated value is known as correlation. Whereas Parameter is not a dynamic value captured from server response but it is something for which the user has predefined data values available.
We can use web_reg_save_param function to identify those dynamic values, but web_reg_save_param function does not perform correlation. web_reg_save_param function just registers a request for correlation from the next server response. That's why web_reg_save_param function should be placed before action functions, such as: web_url, web_submit_form, and others. This function is used often.
We have two more functions like Web_create_html_param & Web_create_html_param_ex but these two are just used for backward compatibility.