There's no way you can do a good wheel alignment by hand. If it comes out right, it will be purely accidental. You can't just eye things up. If that were true, I would never have bought a 50k alignment machine, and a matching lift. Here's a few problems you may run into.
You must first do a runout compensation. Without that, all your measurements will be off. If you set tow and are off by just a few mm's, your tires will wear out a lot faster than normal. Then there's camber. Like toe, you can't just eye it up with no runout.
Alignment adjustments are not isolated. When you make a change to one angle, the others change as well. If you change caster, camber or sai, toe moves a lot. The amounts vary from vehicle to vehicle, but on some cars you have to adjust caster, camber and tow at the same time. Without some type of machine, its impossible. But you can't even get that far without doing a caster sweep. Caster sweep is necessary to get caster, sai, included angle, toe out on turns and sometimes camber. So, just to be clear, if you do a string and board job to adjust toe, at the very least, you changed camber as well. I almost forgot, in order to do a caster sweep, you need to have the front tires on slip plates. If not, you'll have too much friction to do an accurate caster sweep. Also, slip plates have marks that are used to measure how many degrees you are turning the wheel. You need those readings as well.
Its good practice to have heads on the rear wheels, as well. Even if you have a solid rear axl. The rear heads allow you to measure thrust angle. You need to know where your rear wheels are pointed in order to get a straight steering wheel. Technically, having a straight steering wheel is cosmetic, and its not part of an alignment, but if you give a car back to someone with an off center steering wheel, they usually flip out.
I know that I'm new to this website, and no one knows me, but I've been doing wheel alignments since I was 14, and I was a wheel alignment instructor for over 10 years. I've owned or used every machine on the market. If anyone is going to have an alignment done, post and I'll be happy to tell you what adjustments are on your car. if you're watching the mechanic, I can list every step he needs to take, in order to do a good job. And you should watch while its being done. If a car comes in with a straight steering wheel, there's no way to tell if it was even done. The before and after printouts they give you can be faked in a matter of seconds. I could put your car on the rack, and instead of taking the time to do the job, I could fool with the heads and put everything in the green, and hit the print button. I can say, at the very least, 75% of all mechanics do this on an daily basis.