For those who are not familiar with On Target, I'll say this: It's really a great way to keep track of what's what during load development, especially if you test at 100 yards. All the deviations are there at 100 yards, but they're small of course. But by making careful and accurate measurements, you can properly evaluate all the variables involved in proper load development. Here is the basic idea.
You shoot any target you want, commercial or one of the built in targets that come with On Target. I prefer to print my own special targets 10 to a page of letter size paper, usually card stock. I normally shoot one five shot group per bull's eye, so one page is good for 50 rounds. The pages are small enough so that I can staple up 4 targets at once and not change targets for 200 rounds, which is more than enough in most cases, even if you test several rifles.
Anyhow, when you're done you take the targets home and scan them. Or, if you prefer, you can photograph each target with a camera or a smart phone or any other method which will produce a jpg file. You open the jpg file in On Target and, assuming you made a photograph, you first scale the target. That is much easier if your target has a 1"grid in the background, but a known size anywhere on the target is sufficient.
You tell On Target things like range, bullet diameter, and so on. You use your mouse to mark the aim point and the position of each bullet. You can easily do this to an accuracy of a couple of thousandths of an inch which is way better than a coin or a carpenters tape.
Then you save that target and go on to the next. The program can output several types of data but I like the CVS files which I import into a spread sheet. I get the date, an ammo batch which I code with a number, the X and Y deviation of each shot, the MOA of the group and best of all, the Mean Radius.
Mean Radius is a real PITA to calculate by hand, but it's child's play with On Target and is usually more meaningful than MOA when it comes to comparing things like powder charge tests. I add to the CVS file things like powder type, bullet weight and brand , charge weight, and any other important notes using the same format each time. Then I save that file for future reference.
I copy the data and past it into a master file for that particular rifle and barrel. Then I can sort the accumulated data by things like Bullet weight, Powder Type, and Mean Radius. Sometimes I ask Excel to average the 5 or 10 best results for each of these categories. Then I can decide how an 80gr Berger VLD with several powder types compares with a Nosler 80gr RDF with the same powders. You get the idea.
The point is that if you use On Target software you can at least get precise measurements of your group sizes. With a little more work you can perform sophisticated sorting routines and accurately compare apples, oranges, bananas, poodles, and rocket ships; i.e., anything you can imagine. Try that with a tattered spiral bound notebook.
If I had to have only one tuning aid, I'd give up Quickload, all my ballistic apps, my chronograph(s), etc. and keep On Target. It's the single best tuning aid I own.