Are you guys talking about this?
www.archerrange.com
I got this free from the owner (he was giving away free samples, and I happend to luck out on one! [8D])
I have played around with it and, honestly, it DOES work. I'm not sure about hilly terrain or side slopes, but on level ground, it works great. It "does the math" for you, so you don't have to second guess your range.