Re: Estimating the gain from a graph for a invertng amplifier
From basic Calculus, the partial derivative is the slope , measured from any graph by Δy/Δx.
For ease of mental calculations, use an Δx integer or the intercepts on the X axis to view the Δy difference.
One can also average the slope from multiple points to improve accuracy of reading graph.
If random estimate/measurement errors , the result is improved by root of number of samples is from statistics or drawing a straight line and extend the line to both axes.
This method is also used to measure active component effective series resistance (ESR) when saturated from V-I curve.