Steve,

I went back to look at the specs for ADuC834,

Analog Devices claims 24 bits with no missing codes at 20 Hz. But they have another section where they back off on the 24 bit claim. At a range of +/- 20 mV they claim 13.5 bits and at +/- 2.56 V they claim 18.5 bits.

So, I would agree with all of the statements made on this subject, 24 bits is not achieveable without going to elaborate and expensive measures and as you said even then the precision and long term repeatabilty of the measurement will be suspect.

Jacob