Let explain how its done a little better.
Here is your trim die:
That's the 7/8-14 nut that gets replaced with a Hornady locking ring. I use the cut on the locking ring as a reference when adjusting.
If you want to save yourself a lot of time setting up sizing dies, and want to do it correctly; get a Hornady Heaspace Gage. Or, you can just buy the insert because it uses the same head as the bullet comparator if you already have that.
I adjust the die down coarsely until I see that the neck is getting sized all the way down and the die is getting close to bumping the shoulder. Then I start measuring the shoulder with the Hornady gage and start making fine adjustments down. You know you're getting close when you start to see the shoulder grow a bit. The body is being sized, as is the neck, and the shoulder is bowing a bit (this is why "partial" resizing is a bad idea). I eventually see the shoulder go back to the same position as a fired case. Then one small adjustment and I've got my 0.002" shoulder bump. I then test a handful of case to verify.
To adjust the trimmer, I screw the motor down till it contacts the case mouth. Then I remove the case and adjust it a bit more. I hold it in position and tighten up the nut. Then I turn it on and trim the case and measure. Its pretty easy to judge how much to turn it to cut 0.001" more since those threads on the top are pretty fine. And with the die in tight, its easy to hold the motor still while you tighten or loosen the nut.
I can install and adjust a new setup in about 10 min. And if you lock that top nut, its just a matter of screwing and unscrewing the motor.