The three STEEMIT assets are STEEM, SP, and SPD. Having individual coins/voting power/dollars creates a determined market value against the other. STEEM and SP back/fund the community by speculation in the crypto market. SPD is the debt derivative that grows out of STEEM and SP being a increasingly trusted value of storage/promising tech in that market. SPD is what's spent and cashed out before SP so the middle man of STEEM coin will always keep the other two from inflating or deflating too quickly. If all of the STEEM was sold through the floor, SP and SPD would go down with it, but there is a reason we're all here ;) @dali.soh @inventor16 @acidyo hope this is accurate enough and helps enlighten!