Walls and Ceilings - How do I tell if studs are even?

I need to find out if studs in an open wall are even, or, more to the point, how to even them...

I can't use a level horizontally against the faces right? Right do I do?

To be clear, I'm trying to find out if all the stud faces line up with eachother, thats what I mean by even. Thanks

I've never had to do it, but I've seen it done. Yes, you take a long level or straightedge and place it against the face of the studs horizontally at several heights (say 18" from the top, middle and 18" from the bottom), any studs bowed in would show a gap, bowed out would allow the level to rock.

I think, IIRC, the guy I saw doing it would mark low areas with a "-", high spots with a "+".

As I said..never done it, not a Pro.

Snap a string from one end to the other, mason twine that stretches and pull it tight. Then slide a piece of 3/4" wood under each end to hold the string out away from the studs. Then measure from the string to each area you want to check, hopefully nothing is farther out of line than 3/4". If so, use a thicker spacer. If you need to start right in a corner, you can wrap the string around a spacer and screw it against the wall. Do same with other side and just before the screw pulls it tight against the wall, pull the string tight.

Easier to do than explain,
Bud

"And how to even them...." Cut 1/3 the way through the cupped in side of the bowed out ones, nail ply. gussets on each side(3-1/4x15"), after pulling stud aligned. The box stores sell cardboard shims (4'x1-1/2") for that purpose. Be safe, GBR