Whatever that machine is telling you, is a lie. That's the simple truth. Either you measure wattage on a stationary bike or you measure wattage + speed in the real world. You don't measure speed or distance on a stationary bike. Wind resistance is a huge part of cycling that you're not even experiencing on a stationary bike.
And since power meters are typically in the $2K+ range for meter + head unit, you don't have that in a gym and as a casual rider you won't have that either. Get on a real bike outdoors if you want to log miles on a bike.
For example, if that machine was 110% accurate, you'd be a TdF professional - http://home.trainingpeaks.com/races/team-sky-races/2011-tour-de-france/stage-2.aspx
He's averaging 430 watts in a TT for ~24 minutes. You're saying you're producing 30 more than that for twice the duration. You're not.
