What is the correct height for a chair rail?

What is the proper height that a chair rail should be?

We Install It At 36" From The Finished Floor, I Have Seen It At 32", But Not Much.

I would try 1/3 of total height of wall
if u are going to use it as a chair rail I would put a chair up to the wall and see where it hits
or see what looks the best where it may intersects other trims etc.
get r donehow about a rating?