Using BF calipers is a skill just like using a knife sharpening stone;
just because you have the knife sharpening stone doesn't mean you know how to use it properly or that if you do use it your knife will get the "razor's" edge you are looking for.
You can get reasonably accurate measurements with calipers, but you will need to practice, and consistancy is key.
The more points you check, the better approximation you will get.