Visa has released a new iPhone app that uses survey data to help parents calculate the going rate for tooth fairy emoluments, based on a parents' gender, age, income, location, and educational attainment. The Atlantic's Alexis Madrigal played with the app for a while and came up with in interesting discovery that doesn't really surprise me much: The smaller the amount I put in for household income, the greater the size of the average tooth fairy's gift. In fact, I was only able to get calculator to output $5 by setting my household income to $20k per year and selecting that my...