Operator interaction effects.

The device will also be evaluated with respect to: (a) The degree of sensitivity of device effectiveness to variances in installation, operation and maintenance; (b) The adequacy of manufacturer-furnished instructions for minimizing variances in installation, operation and maintenance; (c) The extent to which device installation or use, or the effects of such installation or use, relate to Federal emission control regulations; (d) Effects on the performance, safety, or occupant comfort of the retrofitted vehicle, and on that of other vehicles; and (e) The relationship between total cost of ownership of the device (purchase price plus maintenance costs) and the cost savings realizable from its fuel economy effects.