Craig said they've increased (or is that decreased?) the tolerance in their tests, so they're probably junking more at the factory and passing along consistently better ones. They may not have been looking for a problem, just a solution; if extra testing is the solution and they don't care about why they need to do the extra testing, that's good enough for me.
Is this question based on the knowledge that the nub producer has found what went wrong?
I'm pretty sure that ED mentioned that they were stress-testing them very ferociously now.
EDIT: Bah, ninja'd. That was meant to add to Stan's point.
Maybe the stress-testing itself helps rule out the defective nubs. I found this article:http://findarticles....4/ai_n28649499/
It gets very technical half-way thru the first page, but theres some interesting details before that:
The results of these studies have shown that:
1) Strain level affects significantly the electrical resistivity.
2) Virgin (previously unloaded) conductive elastomers undergo an irreversible process when loaded, therefore their electrical response in subsequent loading cycles may not be predicted.
3) Electrical response of conductive elastomers can be stabilized by mechanical preconditioning applying cycling loading procedures. Conductivity properties of mechanically stabilized specimens are nearly reversible when subjected to strains below 50% of the previous preconditioning strain.
4) In relaxation experiments of stabilized specimens the resistivity ratio changes with time in a fashion very similar to changes in stress.
I think that the bolded part may be the cause of the problems. If the nub conductive rubber is not stress tested, even if it is perfectly made, then when it is first used it will change it's conductive properties, irreversibly. This may end up causing some defective nubs.
But after stress testing it's possible to rule out the nub rubbers that don't work. Also after proper testing, the nub rubber should stabilize and continue working properly (the ones that pass testing that is).