With practice, you may be able to measure any pin gauge and determine it's size to the nearest .001"
If you get really tricky with a dial caliper, you may be able to tell if it is a "+" or "-" gauge, that is +.0001" or a - .0001". That trick requires everything to be done right:
1) Calibrate [screw on the dial face ] the calipers with a pin gauge very near the size to be measured.
2) Wipe off the jaws
3) Get the jaws square on the gauge to be tested.
4) Get the test object at the same location on the jaws.
5) Use the same force as during the calibration.
6) Find the spot and the force of greatest repeatability
7) Not every $20 Chinese dial caliper is capable of this, but some are.
8) Don't drop the calipers.
9) Get good by using your dial calipers for competing with machinists with their micrometers.
I buy + pin gauges:
up to 1/4"
http://www.use-enco.com/CGI/INSRIT?PMAKA=890-9739&PMPXNO=5215207&PARTPG=INLMK3
1/4" to 1/2"
http://www.use-enco.com/CGI/INSRIT?PMAKA=616-8130&PMPXNO=5215208&PARTPG=INLMK3
These are actually handy in handloading.
Placed in a collet bullet puller in a single stage press, they can be used as a powder compressor or as a neck mandrel, or as a primer pocket go or no-go gauge.