Yes, they measure Cartridge/Brass for size & fit. If the shoulder is set back too far (Longer from the opening to the shoulder), it would not detect it. If the other was the case, where the shoulder was too long, (Too close to the end of the case), it would detect.
I got started with them when I was having problems with 300 WM bullets at 3120fps causing some reshaping.So I knew if I needed to Full Size or not. Usually I full length resize anything that is a Bottleneck, just to ensure the shoulder. After some of the quicker loads, yu may need to trim to spec length. The Wilson will let you know when this is needed as well.
Good Luck