It's been a while since the last post on this thread but I found a link with some information relevant to these types of range finders. They work on the average chest size (

) (can't wait to hear the comments on that one) of the animals. The link to the article is:
http://www.chuckhawks.com/kill_zone_game_animals.htm. There is some interesting reading in the article. Just in case that link goes dead I'll include the dimensions on North American game animals:
Pronghorn antelope.................= 14"-15"
Small deer...............................= 14"-15"
Medium size deer.....................= 17"-18"
Large deer...............................= 18"-20"
North American wild sheep.......= 20"-22"
Mountain goat.........................= 22"-24"
Caribou...................................= 24"-26"
Elk...........................................= 24"-26"
Moose......................................= 30"-36"
Happy hunting!