This topic has been covered before, but I thought I would share my opinion. I thought I would explain it in layman's terms to make it easier to understand the basics. A bullet passes the line of sight twice as it travels. Think of it like a football being thrown down field. You will have a near zero and a far zero. For the average .22LR high velocity round used for squirrel/rabbit hunting and plinking, it will pass the line of sight at 20 and 60 yards. With that said, when setting zero on your 22, set it at 20 yards first. Then go to 60 yards and fine tune it if necessary. This will put you at minute of squirrel out to 75 yards. For the average centerfire non-magnum round used for deer hunting, it will pass the line of sight at 35 and 200 yards. With that said, when setting zero on your deer rifle, zero at 35 yards. Then go to 100 yards and adjust windage if needed. This will put you at minute of deer out to 300 yards. This is what I was taught 30 years ago, and I have had great success using this simple method. Obviously, your specific needs may require you to set zero at a given range, so mileage will vary.