Below is the H1 of the Example Document,
Safe Keyword Density for SEO
For well Optimized tag the selected Keyword for the Page is Keyword DensityHow it's works
Here the chosen Keyword for the Page is Keyword Ratio
This tool has the ability to check with different keywords and gives the report about how it's optimized for the particular Key phrase. Using Key phrase in the tag is better chance to in front of SERP in various keywords.
Latest modern Search Engines like Google using some synonyms terms that matched to our word so use synonyms of the Keyword in this tag.Updated on Sep 03, 2015