In both coin/jewelry & Relic modes the Dual Control only affects discrimination.
When the detector is used in the prospecting mode, the Dual Control affects the S.A.T. SPEED for gold nugget hunting.
This is the speed at which the machine detects the ground mineralization and ground balances to phase out the ground.
In coin/jewelry & Relic modes, the SAT is fixed and cannot be changed(fast tracking). It is adjustable while in Prospecting mode for serious nugget hunters because of the rapidly fluctuating ground mineralization common while prospecting. Also, if the ground mineralization is very low, you would rather the detector not update the ground so quickly as the threshold is much smoother if the S.A.T. is lower. If you are using the prospecting mode and set the S.A.T. control too high it will become unstable and jittery since it is trying to accommodate for mineralization too quickly. While in prospecting mode if you turn the S.A.T. control down low, it tracks the ground more on a slow average basis instead of updating rapidly.
If you are not using the prospecting mode, just ignore the S.A.T. function of the dual control. I assume you are not confused about the discrimination function of the dual control while in the coin/jewelry & Relic modes.