Get a stronger stud finder. My walls are drywall then plaster. Almost 2” thick in spots. A regular stud finder does nothing for me, but I’ve got a higher end one that can find them.

Otherwise the old outlet box trick is a good way to start.

Measuring 16” from the corner isn’t a good way because the wall probably isn’t a perfect multiple of 16”. That corner could have been the end of the wall when they framed it. A 170” wall from the tail end is going to have studs at 10”, 26”, 42”, etc