How to measure pillars vertical angle stand

Making a small shelter of my own wasn't so easy task and there are quite a few thing to think of to get it done properly. One of the most important aspect to consider is the pillars vertical standing position. Merely using bare eyes and common sense might result in the pillars a little bit offset from the vertical position and causing it to slanting down. This can have problem later on when putting the pole and the pillars position is off the marked from one another. So to solve this is to use pendulum or a metal object. Punch a nail at the top of the pillars as the suspension point and hang the pendulum on it - if it follows the pillars exact center that means it is perfect vertical otherwise if it is on away from the pillars it's not vertical. Use a heavier object as the pendulum and it is more accurate when the gravity work on it.