There's a rough 25% efficiency for human work and this is conveniently the conversion of kj to kcal so if a PM reports 2000kj you can basically say that's 2000 cals. Something like that. I basically eyeball the kj number in WKO and that's my cals used.
It says 2,329kJ. A friend I rode with has roughly the same on his. Both with measured HR and he has a PM
Kcal roughly 0.24 x KJ I believe
Edit: I see now it does tell me calories actually
Calories: 3,361
I wonder how that amount of work done can turn into that number of calories burned then