Gogle Dance: How to watch Google update

Many times, we want to know when GOOGLE updates, such
My website has just added many pages, hoping to know how many pages GOOGLE will Index next time
I just made a connection with several good websites and hope to know if the PR will last longer after GOOGLE's next update.
If you want to regenerate the HTML page of a website, you should avoid GOOGLE update, because GOOGLE may delete the page due to excessive 404.
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How do I know when GOOGLE will be updated?
GOOGLE researchers found a simple way to check whether several GOOGLE image sites are the same, because during the GOOGLE update processWww2.google.comOrWww3.google.comDuring this period, the number of pages indexed in the last two sites is different from that of the primary site. For example
Www.google.com/Www2.google.com/www3.google.com
When the three websites search for the same keyword, the number of results is different, which indicates that GOOGLE is updating.
GOOGLE's large-scale update, known as google dance (dancing) abroad, has a website dedicated to helping us check whether he is dancing.
Http://www.google-dance-tool.com
This website provides a tool. With this tool, you only need to enter a keyword and click a button to view the search results of the three GOOGLE image sites, which is convenient for us to compare.
Through this method, I learned that the last GOOGLE update was in early January and early February. My friends and I witnessed a change in the number of pages indexed by GOOGLE on their respective websites. Last night, I checked and found that the search results for the keywords "statistics" and "download" on the three image sites were different, indicating that GOOGLE was active again.