If you true bicycle wheels using dial or digital indicators, you’ll know the joint area can be problematic on some rims. A little twist or bump can wreak havoc, sending your instrument to the moon albeit momentarily. I’ve revised my process a little to manage this problem.
Normally truing is oriented from the valve hole. Start at the valve hole and continue around the wheel until returning to the valve hole again. There’s nothing special about the valve other than being a signpost so you know you’ve covered the whole wheel. Now I start at the joint. Begin scanning immediately after the joint and continue around the wheel until returning to the point immediately before the joint. This factors out hyperlocal distortion at the seam. The only problem is there’s no signpost to indicate the start/stop point. As an aid to memory I install a little peice of masking tape, which does the trick.