The devil is in the details. A stated 0.02% 'basic DC accuracy' is not a complete spec.
I'm very well aware of that, but that is how data is usually presented everywhere, including Fluke website
I am rather on conservative end when it comes to datasheet performance. While my old APPA 72 has "only 0.5%" is it far more stable than cheap chinese no-brand multimeter which drifts with battery depleting.
No reasonable multimeter with 0.0X% spec will drift with battery voltage. Only the king of multimeters, that is DT830 is allowed to do that.
Most magic question for me is what hobbyst application calls for 0.03% accuracy and how to validate this accuracy in hobby environment?
Simple, It's called "I want". Actually 99% of the forum discussions here is based on precisely that application.
I appriciate AN870 declared accuracy, yet I do not trust it too much in long term...
Any references to that? Other posted provided evidence that it's fine.
2) What manufacturer? https://anengmultimeter.com/ Sells clothing... Aliexpress shop?
Manufacturer is irrelevant, unless you buy your Fluke for status, that is.
3) Reference is only one thing among many responsible for accuracy. None is particularly recognizable or look stable
Reference is probably most important thing still, look at any teardown Dave does, reference always gets lots of attention. And also how do you determined that its not stable?
Is it resistant to radio interference? Rather not.
Why this matters? I'm not sure that's common design criteria for multimers.
1) Manufacturer does not provide anything remotly similar to proper specifications. What is long term drift? Nobody knows.
Whats long term drift on Fluke? I doubt anybody knows either.
But if I take it for a 50-mile drive out in the mountains and while testing some equipment (indoors, room temperature) I take a measurement of 7.492V, what is my confidence level that this reading is accurate to within a certain amount, say 6 counts?
What kind of guarantee Fluke provides here? Do they spec their multimeter for altitude?