I'm sure if one sampled the mass of human thumbs they'd find that it varies by more than 5. $1/watt/year is based on a typical $0.12/kwHr US electric rate, but

I'm sure if one sampled the mass of human thumbs they'd find that it varies by more than 5. $1/watt/year is based on a typical $0.12/kwHr US electric rate, but even that varies by a factor of three depending on location and usage category.