Thanks alm for that historical perspective. Each paragraph in reply to bolded items.
Was doing some research after reading your post. I see the 8508A is a metrological DMM, a truly super meter, with amazing specs, and a price to match, ~ $10,000
used ![Shocked :o](https://www.eevblog.com/forum/Smileys/default/shocked.gif)
and sadly the 'net says its discontinued. Amazing, it was built back in 2002. By comparison, a new 3458a as a basic DMM is $8000, new, $9800 with the high ppm stability board. Going rate at eBay is ~50% off.
![](http://www.hartscientific.com/images/8508A.jpg)
I can see why. I'm not sure what the 8508a ran for when new, but it seems for calibration use, there's nothing like an 8508a, its accuracy is even mentioned in confidence intervals, which is really the most precise way to mention accuracy, and its AC accuracy is peerless.
In the HP 345x pedigree, there is a leap in accuracy between 3455 and 3456, not from 6 to 7 despite the higher scale reading, and again a big leap from the 7 to 8. As a simple reference, the 10V scale [ 30V for the 3457a] at 90 days all converted to ppm, including the LSB:
345x ppm |
5 51 6 25 7 54 8 4.15 |
Yes, I guess because of the current range so the 6 is not really a 'complete' DMM? But the amp accuracy on the 7 is low, a good handheld is better. Its LSB count error is absurdly high.
Yes, the 3457a go for more, given the added capabilities, I presume beyond accuracy. I'm comparing the final purchase price, whether it be buy it now or bid, whichever is lower from eBay. Also comparing unit equitably whether its for parts, working but not calibrated, and calibrated.
The Fluke HP 3458A had better specs than the HP one (though I believe the difference was just one resistor). The Fluke 8508A is currently the most accurate general purpose lab multimeter, as far as I know.
It's kind of funny. For 'normal' folks like us, the HP 3458A is like the holy grail of lab multimeters. I was reading the PMEL (army/air force/navy calibration lab) forum, and they complained that the 3458A was useless for anything but DC, and preferred the 8508A.
The HP 3458A is fairly old (1989 or so), from memory, I think the 3457A came out in 1986/1987, and the 3456A in '81, not sure about the 3455A (late seventies?). I would have expected a 3459A somewhere in the past 20+ years.
Does the 3457A really fetch $200 more than the 3456A in similar condition? They both have some pros and cons, no clear cut winner as far as I'm concerned. I had a choice between a 3456A (tested, good history) and 3457A (lightly tested, gave calibration error about current range) for $50 extra. I chose the 3456A because of the better display and better stability, and because the current range on the 3457A was probably bum anyway. So in my opinion, the prices should be pretty close. The 3456A was more expensive than the 3457A when both were current products, and the 3455A was even more expensive.