That's a little bit different than a chart I found a few years ago. This one says:
The old formula (1 dog year equals 7 human years) has been updated. A better calculation counts the first year of a dog's life as 15 "human years." The second year of a dog's life equals 10 years, and every year thereafter is equal to 3.
For example: A ten year old dog would be:
15 + 10 + (3 x 8) = 49 "human years" old.
