Is SEOCentro’s Keyword Density Tool Accurate?

In episode 194 of Semantic Mastery’s weekly Hump Day Hangouts, one viewer asked if SEO Centro’s keyword density tool is accurate.

The exact question was:

1. Had a question about using SEOCetnro to do our keyword density checks. I notice that it takes into account all tabs also for keyword density. It also is pulling additional keywords that I can’t find anywhere, so wanting to know if it is accurate and if your still using this service for keyword density.

Here is an example. SeoCentro shows 9 instances of “”concrete grinding”” and I for the life of me, can only find 6 instances including in the tabs, but it is saying there are 9. http://www.dynamitecontractors.com/services/concrete-grinding-surface-preparation/ is the url in question. Any clarification would be great.