I just bought this item and being new to reloading I have a few questions! I understand the setup for measuring the length of a once fired brass[ 340 Weatherby ] in my rifle. From what I've read I want this cartridge to headspace on the shoulder and not the belt for long brass life and safety. I take a reading of length on the caliper dial and then what? I know I am suppose to set the full length die so it sizes this brass to this measurement but not sure how. Any suggestions would be appreciated!

Screw the die in until it just touches the shell holder, when the ram is cycled through TDC, and than unscrew the die 2 full turns.
Lube the body of a fired case (do the inside of the neck also), but NOT the shoulder/neck (to avoid dents), and run it through the sizer. Note how far down the neck you have sized and compare it to a fired case with your "Stony Point" thingy. Screw the die in, just a little at a time, until the shoulder is pushed back .001-.003 from its fired position. When you get the "setback" you desire, tighten the locknut into position and verify the setting one more time. That's it, your done.
1 full turn will move the die/shoulder position .071
1/2 turn will move the die/shoulder position .036
1/4 turn will move the die/shoulder position .018
1 "flat" will move the die/shoulder position .012
1/2 flat (point to flat center) will move the die/shoulder position .006
The above assume a standard 7/8-14 thread on your die.

I find it quicker and "usually" just as close to smoke or color the shoulder with a magic marker and resize the case in increments as posted above until the soot or ink is wiped off most of the shoulder. Brass springs back a bit so just because you note ink being removed doesn`t mean the shoulder is setting back.
I do check with my stoney point when I start removeing ink just to insure I have it right. You don`t have to repetedly remove, measure and replace and size this way and can find the proper seating depth of your die in a couple of minutes max.

Thank you! I will give it a try!

Joe
It sounds like we do it in the same manner, I just didn't feel like typing out the details of "neck smoking" and the "short cut" of eyeballing the neck until it's close, before going to the gauge (besides it gives him a excuse to play with his new toy, the SP gauge).
I gave the change/turn numbers so he would be able to adjust a little quicker (you want .080?, go down 1 full turn and check again, etc)