Or better yet, pay for results, not hours - if only results were always easily measurable. If A and B have the same base productivity assuming they work the sam

Or better yet, pay for results, not hours - if only results were always easily measurable. If A and B have the same base productivity assuming they work the same amount of hours, B's productivity per hour might be less if he works 70+ hours and A works 30 hours. So it might not be fair that they're then still paid the same per hour.