In the forum archives many users have reported differences in times recorded on different machines - most notably between new machines or machines with replacement cords compared to well-used machines. These reported experiences are always dismissed by other posters as "psychological".
Continuing the reasoning of my previous posting, and using the same figures, here is an easy to understand illustrative example for those still in denial about this: Let us have a 500M rowing ergometer race between two people. The two ergs being used will have the strength of their elastic cords measured to ensure that the force required to stretch them is identical. This is important because, as stated, the monitor does not measure the energy to stretch the elastic cord, so the force to stretch each cord must be identical on both machines, a constant, to guarantee that the race is fair - any difference in cord strength and it is no longer a level playing field.
In this race however, a 20 pound bag of potatoes will be suspended from the high 30 foot gym ceiling, and one of the ergs will be connected to it so that over the course of the 500 metres the person on that machine will have to hoist that bag of potatoes almost the full distance from the floor to the ceiling. Will this race be fair? If both competitors expend the same amount of energy, then according to the monitor, will the competitor required to hoist the bag of potatoes win or lose?