GPS.
Averaging?
And bear in mind, folks: According to Dr. Oz (and he should know), for every 35 pounds you lose, your penis appears to grow one inch.
The day after he said this on TV, gym memberships skyrocketed.
I’d suggest a 12-inch ruler. Though, for some of us, that may be insufficient. 
Actually, this does speak to another advantage of the metric system. The number does just kind of sound better.