exercise calories using HRM

happyindian

We have precor machines in our gym which also displays heart rate. so , i am taking it that they show calories burnt on the basis of the heart rate. will those be accurate or at least a better measure than the machines without HRM.
Also, when i log my effort into MFP, it always says less than what i have 'actually ' burnt, meaning what the machine says.. I was wondering how does MFP know what incline or resistance my machine was set at. So ,are MFP calories just a generalisation???