For me, installing the Tune-o-Matic bridge on my electric guitar was rather scary. This is because if your measurements are off, the guitar's intonation will be off, and the guitar will be out of tune on the high part of the neck. So here is my method for installing a Tune-o-matic bridge.
As you can see in the photo below, I temporarily installed two tuners on the electric guitar's headstock. One on the low E, and one on the high E. Next I to a piece of scrap 2x4 wood and cut an arch in it to match the shape of the bottom of my electric guitar. It can be seen in the bottom of the photo below.
I then took the stop bar, and two nails and mounted the stop bar as shown. I then strung the high E string where it normally is strung, and then a took a B string and strung it up in the low E position.
Now with this setup, I can slide the 2x4 in the bottom of the photo to the left or right to properly align the two strings over the neck.. The goal here is to have each string equally spaced down the middle of the electric guitar's neck.
Once I have found the proper location, I just clamped the 2x4 down.
Also, in order to protect the edge of the electric guitar, I placed a piece of cardboard between it and the piece of 2x4. If you look close at the photo on the left, you can see it.
Here is another photo showing the guitar strings properly aligned with the electric guitar neck.
Next page: More Installing the Tune-o-matic Bridge