These are excellent questions and probably by far our most frequently asked questions. Unfortunately, a quick answer cannot be given. First, let me explain the numbering scheme. The 400 in the name means the range finder will range to trees at 400 yards away.
Trees are neither the best nor the worst targets for range finding.
Lighting conditions - low light gives the best ranging conditions. Target size - the bigger the target, the better chances of ranging to it. Hand steadiness - this factor will obviously vary from person to person. A fun trick I tried with coworkers some time ago involved holding a laser pen pointer steady on a wall 30 feet away. You will be surprised at the amount of movement.