Hi, sorry I didn't post back about what my vet said! I asked the vet techs how they get the weight of the whole iguana, when the tail wouldn't fit on the scale they described to me. They say they use an open topped container; weighing it before hand and then putting the iguana in to weigh it, subtracting the weight of the container. Also, I found a cool website of veterinary scales! The cheapest one is $119.00. Not bad, it you're going to use it all the time.
he vet techs said to use one that weighs in grams, but personally, that doesn't mean a whole lot to me in practical terms. I like the method somebody suggested of weighing yourself, then you with the ig, then doing the math. 
http://medicalscales.com/vet/
