Calorie difference between 2 apps

bndcksaint62

I have been using a bluetooth HRM for my running, spinning and elliptical, yesterday I did an experiment running 2 apps to compare my calorie burn using runtastic and digifit. Digifit is using my 30 minute cp30 cardio test, runtastic I'm assuming is using my general information, my question is, and my heart rate between the 2 apps are 2-3 bpms, so no issue there, why would digifit say I burned 412 calories for 40 minutes and runtastic says I burned 289 for the same amount of time? Any input would be greatly appreciated, thanks in advance