Mile Markers

We drive all the time on I-25 (OK not ALL the time).  You would think that we would know how the numbers for the exits go, and what the exit number we use all the time would be.  In fact we drove on I-25 twice this week alone...  But sadly we do not know...  I know silly post, but intriguing question.  So which way DO the numbers go?  And what mile do we use most often?