Producers risk: The probability that a good lot is rejected.
Consumers risk: The probability that a bad lot is accepted.
AQL: Acceptable quality limit. The maximal percentage of defects that is still considered acceptable.
RQL: Rejectable quality limit. Rejectable quality level or poorest level of quality that the consumer is willing to tolerate.
The curve indicates how many history samples (i), the x-axis we need to respect the acceptable quantity limit (AQL, y-axis)
The AQL is indicated by the red line. The blue line indicates the risk per amount of history samples.
To find the amount of history samples we need to respect the AQL and keep the risk as low as possible one must find where the blue line crosses the red line (Optimum).
The current situation is indicated by the green cross. If the green cross lies left of the black optimum dot. The sample size needs to increase to have as low a risk as possible.
If the green cross is at the right of the black one, it means that the current history samples are enough and the sample size may even be lowered.