Hi, I have a few questions regarding Treasury Bond futures. I understand that every bond that is eligible for delivery into a Treasury futures contract has a conversion factor, where the conversion factor is the approximate price at which $1 par of a security would trade if it had a 6% YTM. 1) Does the conversion factor for a specific bond change over time? If so, what factors cause the conversion factor to change for a specific issue? 2) If all bonds are "normalized" to a 6% YTM using the conversion factor, why would one bond be cheaper to deliver than another bond? 3) What factors would cause the cheapest-to-deliver issue to change from one time period to another? 4) The Dec09 30-Year Treasury Bond futures was trading at: 121'30. How do you convert this into an implied interest rate on 30-year bonds? How does one interpret this interest rate? Is it the 30-year spot rate now or the 30-year forward rate at Dec expiration?