In the measurement report, which I ordered in advance for my 10ppm resistors, they did not reveal the method, but obviously used a 1kOhm reference resistor, specified -2ppm. The designator of this standard is '1500 G 103', maybe something from ESI.
I assume, they used sort of a bridge, but that would be a 11:1 relationship, maybe explaining the extra error.
They measured each resistor three times, adding 2ppm for each value.
Everything inside three times of plus or minus 10ppm was accepted.
For my 5 resistors, they produced a total of 27, and 20 were 'good'.
Maybe they are using a DMM for bigger tolerance resistors.
Frank
PS: I ordered 9k9998 resistors. Vishay measured them to have values of +7 , +8, and three times +6ppm, greater than the default value.
The relative deviations were correct, but it turned out after several comparisons with calibrated resistors (quarks, acbern), that these all deviated in the other direction, i.e. instead they must have had about -14/-13/-15ppm of nominal. Something went completely wrong there.