I lost 10 pounds in 1 week on weight watchers. Is this normal?

Two weeks ago I joined Weight Watchers. The program promises an average of 2 pounds per week loss. This is very healthy. I started at 192 pounds. The first week was fine, but this week I dropped 10 pounds and now weigh 180. Thinking something was wrong with the scale, I tried other scales and they all gave me widely different weights, so I can't eve say if my scale was off. Is it possible to lose 10 in a week? Is this normal for Weight Watchers in the beginning? Is there a way to tell if my scale is just broken? Also, with the diet, I began low-impact exercising at least 20 minutes everyday. Thank you for any help.