gazelle machine / calories burned counter is it accurate?

i have one of those tony little gazzelle machines, it has one of those counters on the top to display, speed, distance, amount of time you are on it, and of course amount of calories burned, you can put the button to keep it displaying only 1 thing or let it just keep cycling thru showing all of that. well i i do sweat bullets and keep up same intensity and speed and heart rate stays up for a good while after the work out, i wonder just how correct the calories burned calculator on it is, if i do it less intensly of course the number of caliores burned it shows is less than what it shows when i do at a higher intensity. well with workouts then putting it in here despite time spent and the pace im keeping up it says id burned less calories than what the machine says. so it leaves me feeling unsure of just how much i really am burning, am i really not burning as much or am i actually burning more than what it calculates on this site and i unknowingly dont eat back enough of my workout calories. sorry this may be confusing but i just would like to be more accurate idea of my workout progress.