BTW its a vernier gauge ......well no.....there is no
vernier graduation comparison function...
So it really is a
digital [measuring] caliper [or a 6" adjustable spanner]
The published accuracy of +/- 0.001" is acceptable, an experienced machinist well may be able to distinguish by feel with a micrometer down to 0.0005"
It is the
repeatability of the digital caliper that is useful here.....a 1" reamer shank could display as 1.000", and a 1" shaft of precision ground steel may measure as 0.999"...measure each item 10 times and you will get the same repeatable dimension on each occasion
My 6 months old $25.00 Chinese digital caliper absolutely mirrors the dimension measured with my 60 year old $25.00 Polish vernier caliper $25.00 some 60 years ago was about one weeks wage]........
Either a vernier caliper or a digital caliper would be 9/10's of useless if singularity used to measure a model engine bore
Derek