[R] Optimization problem

[William Simpson]

Sorry, thought you wanted to find lowest value of x that produced
maximum value of y. I see now that is not the case.

I think you have to decide on what amount of improvement per device
you judge to be 'minimal'. Then the algorithm uses the value of y that
occurs at the point where this criterion is reached.

I think this will do it
min(devices[diff(percentages)<criterion])

Bill