Thanks for the advice ! Just skimming through the book , the only notation that appears completely foreign is definitely the matrices . However other than heavy use in chapter two they don ' t seem to show up again . Chapter two is determination of orbits from observation . <| sep |> Bless you and the quirks of your mind . <| sep |> Walmart Family Mobile uses TMo . You could always pick a phone up from them and pay for a month of service . Alternatively you can pick up a $ 5 SIM at Best Buy and put it in your phone , but you ' d have to have a phone to do that with . <| sep |> 30 bucks for ATHM 20 x . No brainer ? I don ' t like the Monoprice I got , the sound isolation is shit and they hurt my ears . Wanted the m 40 x but $ 45 in my pocket sounds good too . Will I run into the same problem as the Monoprice ones with these ?