I have used a Park Tool TS2.2 on a bicycle course. It has a caliper for each side of the rim. As you turn the dial, both calipers converge evenly toward the rim. This allows you to know which side of the rim has the biggest wobble, and therefore which side needs adjusting next.
Single caliper truing stands measure only one side at a time. Let's say the caliper is on the left. A 'peak' is detected on the left side of the rim, you tighten the right hand side spokes. I get that if you repeat this process the wheel will eventually be true, but you've only tightened right hand spokes. Won't the rim be pulled over to one side and have an imbalance with tense right hand spokes and loose left hand spokes? We were taught not to adjust either side more than 3 times in a row (When needed, the instructor would 'kick out' one of the calipers when he only wanted to use the other one, by wedging a screwdriver underneath the one he didn't want to use)- we would use both left and right caliper, therefore tightening both sides of the spokes, which would be more balanced.
So in my example with the single caliper on the left, the only way to detect 'peaks' on the right hand side of the rim would be to look for gaps on the left hand side, using the caliper as a visual aid. This doesn't strike me as very precise. The only other way being to constantly flip the wheel in the stand. I think there's something critical and probably obvious I'm missing here, help would be very much appreciated.