Thank you, I've seen many many versions of this circuit. I'm pretty new to these circuits, how do I determine the amplification (A)?
If you use a commercial op.amp it is given in it's datasheet.
Given a specific circuit with all parameters of the transistors and other devices you can calculate it.
In both cases it can be measured,
taking care of "problematic issues" in the operation and measurement,
Not the place to elaborate on here.
In the case of a legacy op. amp like the LM741.
The datsheet states a minimum "Large signal voltage gain" of 25V/mV (i.e 25,000)
The typical value at 25C(room temperature) is 200,000 !
They also give it in a graph:
Note,it is given in dB ,106dB=20* log(20,000)
and it is at very very low frequencies under 10Hz(5) !