heyas; the offset a and b are the center points and endpoints. its my hypothesis that they are duplicated in the channels section (there's also a 'center' and 'endpoint' entry after the channels section) for when they become visible with the joint editor. those parameter dials appear when you have the joint editor open. it is similar to when you turn on the 'display origin' for a prop. you get the origin offset dials to move the center via them. the translate channels are the actual movement dials.