Trevithj The reason sources discussing the negative feedback amplifier do not mention set points errors and comparators is that they have no more relevance than the stock market The remarks of Black are perfectly clear and also make no mention of these factors nor do his patents They are understandable as he intended them the use of feedback bypasses the inadequacies of the nonlinear variable and uncontrollable properties of the large gain open loop amplifier as very easily seen in the gain analysis that shows the closed loop gain to be set at 1 as fixed by a resistor divider for example by making the closed loop gain independent entirely of the open loop gain I don t think you fully appreciate the simple algebra that governs this circuit