Joan smiles, knowing exactly what Ted is doing, and knowing Sherlock will be more than happy to show off his knowledge.

"The numbering is particular to the Boeing aeronautic manufacturer," Sherlock answers. "In addition to passenger airliners, they also make everything from fighter planes to missiles. Each category has their own number range. Military aircraft were assigned the 300s and 400s...missiles were the 600s...and passenger jets were the 700s."