I'd been trying to work out how the Concept 2 rower got its calorie calculation and came across the following links

http://www.concept2.com/05/rower/service/PM2_service.asp

http://www.concept2.co.uk/guide/guide.php?article=watts_conversion

• 5000m in 18:39 minutes gives a power output of 250 watts

and a calorie consumption of ((4*250/1.1639)+300)* (18.66/60) = 360 calories (1160 cals/hour)

• 5000m in 18:04 minutes gives a power output of 275 watts

and a calorie consumption of ((4*275/1.1639)+300)* (18.07/60) = 375 calories (1245 cals/hour)

 

This is for an 80 kilo man, for a 100kg man I would substitute 375 for 300, giving ~25 extra calories over 18 minutes. The following links are slightly more complex and take into account your age and weight.

http://www.concept2.co.uk/training/bmr.php

http://www.concept2.co.uk/training/bmr_calculator.php

This calculates that I would burn 454 calories for a 19 minute row at a 1:53 split

A Mars Bar has around 300 calories (449 calories per 100g, normal bar 62.5g)

http://www.weightlossresources.co.uk/calories/calorie_counter/chocolate_sweets.htm