Believe what machine says?

So is the calorie burn stats I'm getting on both a treadmill and an elliptical crosstrainer accurate?

For the treadmill I do intervals so before I start I enter my weight which is 120 pounds and my age of 22. For a 30 min workout I start walking on a 6 incline at 4.3 mph without holding on then every 10 minutes switch to 5.0 mph on same incline and hold on for balance. I do this twice in my interval. The treadmill says I'm burning bout 275-300 calories when I finish.

I strive to keep to my 85% heart rate which is about 28 bpm, on an interval it can jump to 29 bpm.

Elliptical I do a course and set the incline to 7 and the resistance is 7. Strides averages between 160-175 when the inclines goes either up or down for the course program. This said I burned 185 doing 15 minutes today. Same weight, age, and kept to 85 % heart rate. Sweating like crazy and legs wobbly after done.

I'm gonna say working out an hour a day I burn 500 at the gym but I don't want to kid myself if it might not be true so what do you all think? This doesn't even factor in standing and moving around all day at a warehouse 4 days a week (nothing crazy mostly like entering, picking, packing, and shipping orders) so I know I'm burning some there too.

?

Sometime's I'm unsure about how accurate the machines are too, but I think 500 sounds quite reasonable for an hour at the gym. I'm basing myself on the fact that an hour of cycling around (moderate efforts), according to the exercise browser, burns more than 400 kcal and it's less tiring than an hour at the gym.

However, one hour of aerobics (still according to the CC exercise browser) supposedly burns less than the cycling... but aerobics exhausts me completly... so I'm not sure how much I should trust that information. But hey... it has to be more accurate than relying on my guessing. :)