How to straighten a ceiling

[Daniel78]

That's not a bad method.
With that method, it's even possible to use a cheap line laser, as long as you mark a reference point when moving it to a new sweep area.

I think it works quickly and easily, and you only need one single string, the one the laser hangs from in the ceiling

I aligned a ceiling a while ago that required 250-300 spacer washers, in a room about 7*6m in about 2 hours, and there weren't many junctions between beams/rafter strips that didn't need alignment.

The advantage of a rotary laser is that you can hang it in the middle of the room, and in this way, get a good line around the whole room even if you have a cheaper model of laser (maybe it won't work if you live in a castle with rooms of a couple of hundred square meters, but then you get to spend on a more expensive laser