Make no mistake; if I pop out at an overlook and spot a bear across the canyon, I don't draw him before I shoot him If I'm in a long range ambush, I'm usually there for quite a while before I start building a card. I also have some partial cards because I had to break away to take a shot.Good stuff, two drawbacks - you have to know how to draw and have to have enough time to bother. I would argue that spare batteries/kestrel, printed range card and having a mechanical inckinometer would do the trick. My single point of failure is my range finder, but I could always bring a spare
Using range cards will teach you to look at a hillside a little differently. With some experience and attention to detail, a shot can be taken with only the information you've placed on the card.