If you do SEO for a living, you must have a firm understanding of each of these algorithms. While there are hundreds of factors that determine ranking, the six algorithms listed here are the ones you need to focus on. They are the 10% that affect the 90%. You can solve almost every problem a website faces with the information in here.
Do not skip to the advanced tutorials, even if you think you are a pro who has done this for years. Get a solid foundation. A white belt who practices the same 10 techniques every day is far more skilled than a black belt who practices 100 techniques every week.
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Easiest Diagnostics: Compare rankings and traffic drops to officially announced algorithm updates.
Confirmed Updates: http://moz.com/google-algorithm-change
Recent Volatilities: http://mozcast.com/
Another Volatility Checker: https://serps.com/tools/volatility
Yet, another volatility checker: http://serpmetrics.com/flux/