Yeah, I keep track of my BP's weight and measure her length once a week. You should take it to a vet if it starts losing weight. You can get a cheap but accurate produce scale from Target or Wal-Mart for about $15-$20 which can measure mass through weight (g). If (s)he starts losing weight, then I'd worry. Remember, BP's can go quite some time without food. But, monitor that weight! Good luck!