<img src="graemlins/icon107.gif" border="0" alt="[icon107]" /> Do not rule out hardness testing because the dots seem to be found randomly.
It has long been and still is a standard practice to randomly select samples from the assembly line to spot check and perform quality testing.
In the Space Program flight rated parts required that all parts be certified at all stages of production.
Otherwise the testing could be more of a random nature to "Certify the Batch".
I would not expect to find hardness testing done on more than 5% or 10% of the total production.
And I would consider that more than adequate to detect 99.9% of all off standard items, as an erronious series of parts require that there be a "look back" to the last satisfactory items of the series. <img src="graemlins/icon107.gif" border="0" alt="[icon107]" />