The number of energy slaves per capita depends on the method of calculation: either we take the average energy provided by a slave 24 hours a day, 365 days a year, or, as Fuller does, we use the mechanical energy provided by a healthy individual working 40 hours a week (or 3 kWh per week).
The number of energy slaves per capita varies depending on how we measure it: either we calculate it based on the average daily energy output of a slave or, as Fuller suggests, we use the energy produced by a healthy person working 40 hours a week (or 3 kWh per week).