Franco, you reflect my thoughts exactly. Either Sabre is confusing two cups with four, or his 'cup' is a lot smaller than a standard metric (or imperial) cup. It is not physically possible to boil 1 litre or 1 quart of 50F water in the sorts of times Sabre claims.

Paddy Crow brings a sense of science and reproducibility to the discussion "The best way to report the output of a heat device is in power conversion units (BTU per hour, Calories per second, watts, horsepower, etc.). It's relatively easy to do by measuring the weight of the water, starting temperature, ending temperature, and time."

However none of these things tell you how the stove will perform in the real world where wind, pot size, pot material and thickness, windscreen design, ability to simmer, ability to 'snuff and reuse' , stove weight, etc...come into play.