Can an Atmos Expert please explain definitively the purpose and action of the impulse roller spring (#5304) and roller mounting collar (#3507) on the Atmos? Obviously the fork is pushed to one side (providing the impulse to the roller) as the teeth of the escape wheel pass across the faces of the pallets - this is the same in any clock. But most don't have a coil spring. Would it be right to assume that the spring is added to enable the escape wheel tooth to pass more quickly across the pallet face (rather than a less efficient slow drag) and in so doing apply a little tension to the coil spring, which then releases more slowly to propel the roller, taking the balance with it? If so, is the purpose of the collar simply to restrain the coil spring on the balance stem? For that to work, the lower pipe of the roller mount would need to be an easy fit in the main balance stem, with no sense of tightness or friction. I have a 519 where the collar was fitted too high, and seems to have distorting the very top of the balance stem, causing some drag between it and the roller mount just inside it. The amplitude is low and I think what's happening is that the balance is being turned directly by the action of the escape wheel teeth directly on the pallet faces; the coil spring is in effect doing nothing. Thanks in advance.