It means for each year you had at Airtran, you get 2 years of seniority at SWA.
There number one pilot can flip a coin w/ Rice to see who bids number one.
Not quite. First, seniority across carriers can't be expressed in terms of years. Using years as a measurement only works when looking within a single airline. It is meaningless when combining carriers.
Second, it is entirely possible that an arbitrator's award or a negotiated settlement could have included separate categories, such as aircraft with 117 seats or less and aircraft with more than 117 seats. Doing so would dramatically change the outcome.