Hi
Depends what you are trying to measure. Most of the time you will see what is mentioned as snout to vent. This would be the measurement from the fromt of the mouth to the base of the tail, you know where the poop lol Then you can get a total length which is from the mouth to the tip of the tail. You can just grab a ruler and have your cham walk onto it and get both.
Keep in my mind i hate petsmart. I left a store manager job back in the day when they bought out our store. that being said.their veils actually come from the same distributor as flchams. so your are getting the same as what they get. granted, they probably get pick of the litters. it is their jax, that are a little on the hinky side.