The word "tan" indicates equality because it means "just as" or "as".<quoted text>
I'm just telling your what my Spanish teacher say's she says when using Tan or tanto it's a comparison of Equality.
This link say's the same thing but I don't see how.
Raul es tan alto que el.=
Raul is just as tall as he is.
Raul is as tall as him.
Raul es alto como el.
Raul is tall like him.
The subtle difference is similar to the one between simile vs metaphore.