For the California Interstate Commerce Exemption, documentation is critical. You want a thorough accounting of all the aircraft use both before entering California and during the 6-month period after entering. Trips claimed as interstate commerce should include specific details such as business associates you met with, meeting agendas, business cards, or corroborating e-mails. With good documentation this is an excellent exemption to benefit from. Without it, the exemption may likely be denied.