I use one and have had to 'learn' how to use it. Over time I have developed a "touch" which works well. Before the 'touch' development there was plenty of operator error.
First and foremost the durn thing doesn't measure 1.000" across. Mine is 0.996" so when measuring base to ogive I zero the digitals on the nut and measure from there. I don't care about the overall length just the length from the base to ogive. I don't know if the "nut" is accurate for this purpose but things work out well from the reference point determined.
Practice measuring the width of the thing working on your 'feel' and moving the 'nut' around in the caliper jaws. I'm assuming you are using a caliper to measure overall length.
My calipers aren't the most expensive. Heck they may be the cheapest.
My dial doesn't agree with my digital and I don't know which one is correct.
But the differences in measurements are consistent.
When measuring bullet bearing length wiggle the bullet until it has no more wiggle. Then measure and repeat the measure.
When measuring a seated bullet do the same thing but now you have to figure out how to hold the darn thing in the jaws. T'was a bit of a challenge until I learned to lay the "nut" with bullet and cartridge horizontal.
Then you learn that the head of the cartridge drops to the same level as the bottom of the "nut". A bad thing. Rig up something to hold the cartridge head so that the flash hole is centered on the caliber hole in the nut. (There's a better way to explain that but I don't know how.......)
Then when things are level/plumb/etc move the nut and cartridge head in the jaws until you get the smallest reading.
After awhile you catch on and it becomes easier and repeatable.
Good luck and have fun.