I made detailed drawings of the mechanism. After studying it and understanding it, I realized that it is quite brilliant. The design, unlike all of the other single set designs I have seen, does not adjust the amount of sear engagement that the mechanism has when set. The sear engagement is fixed regardless of the weight that the trigger is set to. The sear is designed so that theoretically the trigger pull can bet set to 0 force by balancing the trigger spring against the main spring.
Nomenclature
Unset and normal trigger pull operation. The mainspring rests on extensions of the uprights when in this position, taking it out of the spring balance equation. In this setting, the sear spring pushes on the trigger, and acts as trigger spring for unset trigger operations.
Set for hair trigger. The adjusting screw pulls down on the sear spring, increasing the force on the back leg of the sear, balancing out the force from the main spring that is trying to push the sear open. When in adjustment, the sear spring and main spring are equal, or the sear spring is slightly stronger. When the trigger is touched the slight addition of force upsets the balance between the sear spring and the main spring, allowing the main spring to "win", releasing the sear, and the trigger.
Set showing the sear spring
Some overall views of the model
Mike