Very interesting. I thought that this was going to become the next Voltage Reference system after the 732B/734A system. I never saw any schematics but I never tried very hard. I do remember seeing somewhere in the literature that there were 4ea LTZ 1000A references in parallel in each module. My guesses would be: a. That it was just too expensive for an equivalent system to the 734A. b. That it was too hard to manufacture. Sorting and testing for the best LTZ1000A to use was just too difficult. c. Too expensive when compared to the 734A system. d. No confidence in this system therefore little sales generated. Danaher is only interest in massive profits from the "cash cows". e. The "patented" conditioning system that would allow for cold shipping didn't work out as expected. f. Why change from the "Industry Standard" and proven 734A? g. All of the above. h. None of the above. Bill