Ask HN: Accurately tracking uniques on a high traffic site

The user metric reported by Google Analytics and the StatCounter unique visitor metric are comparable based on the definitions described[1] but I confirmed that the two stats are way off:

Last Month (August) Google Analytics - 1,159,529 users StatCounter - 3,542,476 unique visits

How do you accurately track unique visitors? Which platform is the industry standard?

[1] "A Unique Visitor is a separate/individual/distinct visitor. The sum of your first-time PLUS your returning visitors should always equal your TOTAL unique visitors for the day." (StatCounter) "For example, if a user visits a website on August 31 and on September 1, Analytics recognizes this user as a single user over the course of these two days." (Google) "The estimated number of people accessing a property from online and mobile web in aggregate". (quantcast)