Take two identical dial calipers that are mechanically capable of an accuracy of +/- .001'' and resolution of .001'' with graduations of .001'' on the dial, if one reads 1.236'' and the other reads 1.235'' on the same piece what do you make of it?
You are correct. It is misleading advertising. Nothing new about that, whatever you are looking for. The only way to make it through the mine field is to understand well enough to know how to see through the spin...
I think there is a mistake in the link. The 1. should be +/- .5 I think, the decimal is not holding any precision other than units, since there is nothing after the decimal.And this is what I see through the spin:
The number of decimal places in a readout is meaningless if the instrument itself cannot in fact resolve measurements to that number of decimals or to that fineness of graduation of the readout.
Just like how a speedometer that reads to 250 mph does not garantee that the car can go that fast.
The design of a sliding caliper does not lend itself to making measurements more precise and accurate than +/- .001'' (.002'' total). Plastic or composite calipers probably have special applications (i.e. measuring magnets or delicate materials) but might not be as durable, as accurate nor as precise as stainless ones.
We should be aware how easy it is to be lulled into relying on a digital calliper, that reads to four or five decimals, for accurate and precise measurements. In fact the actual size of the object being measured might be quite different than what the readout is showing.
For work to the last .001'' or less, a micrometer should be used.
Some good reading here: http://www.hobby-machinist.com/threads/metrology-101.22521/