The Archer Range rangefinder's name suits the product perfectly. This rangefinder can only be used out to 50 yards, and only from a treestand 15ft or higher.
Don't ask me to explain the science because I failed college algebra 3 times. There is some triangulation and geometry involved I am sure. Even though I cannot explain how it works, I am smart enough to operate this device. Acutally I think my 8 year old nephew could probably figure out how to use it. Simply climb into a stand at the set height: 15, 20, 25, or 30 yards, point it at the base of a tree, hold a button for 1 second and release. Turn the rangefinder to the side and you will find a range chart. Choose the height you are hunting, (the Archer Range has a convenient built-in tape measure) and you will find a needle pointing to the range of the object. Easy as pie.
There are a few drawbacks to the Archer Range, though. To measure your height, you have to anchor the tape measure to your bag or bow. I anchored to my bag and tried ot use the built in crank to bring it up, but no dice. My bag is not very heavy, but I ended up bypassing the crank, and pulling the bag up by hand. Not a big deal though, still worked out very smoothly.
The biggest drawback, and it is a big one, is that it is not accurate on ranges not level with the bottom of your tree. That means if you hunt draws and valleys, leave it at home.
Overall, the Archer Range is easy to use and very accurate on level ground. With a pricetag of under $50, it is affordable even if you hunt the occasional downward slope.
I give it a 7 out of 10. I would have scored it a little lower, however, the price makes it worth a little hassle.