The image makes it perfectly clear. If I were mounting that 4x4 to the wall and wanted it dead level I would do the following.I'm working on it now. Got the base painted for the wall but am confused on how to line everything up and assure it is level. I need to mount a 4"x4" beam to the wall and have 2 wooden dowels coming out of it. The dowels are going to go into 1 1/4" PVC pipe to support the canopy. Getting it all lined up is the trick. The image below is a poor attempt at showing what I'm trying to do, lol. PVC pipe inside, 4x4 with dowels (cut to size) and lag bolted to studs. Hopefully!
Use a stud finder to locate the studs.
Measure the appropriate distance from the floor and indicate the hole locations using a level. You will need a helper.
Predrill one of the hole locations you just marked.
Drive a bolt partially in and rest the level on it to double check the other location in indeed square.
Make any adjustment needed and predrill the second hole.
Nice looking chair! - Herman Miller?
Should come out dead level.
BTW, I suggest pre drilling for bolts as it is pretty easy to split a 2x4 with a bolt (I've done it many times). It also makes it much easier to drive and keep straight.