How google identify that web page was updated and want to index again?

[ankit.rahevar]

How Google robot identify that these many pages were updated on particular web site?

[FedeEinhorn]

You can return a header last-modified, LastMod in your sitemap, or use the Fetch As Googlebot in WMT and then submit the page to the index.

Even with any of these in place, Google automatically re-crawls your site every few days/weeks or even hours...

[ankit.rahevar]

Thanks for your quick response. Is it good practice if we add "Last-Modified" meta tag on page header.

[Esaky]

You have to update your blog, and when the Google Starts to Crawl regularly - no problem for you.

But you should add the Timestamp in the post or article content. !