For your "independent reviews" of these OHR-A03 (0.01%) & OHR-C03 (0.03%) your best bet, is to surf the Chinese forums.. it ain't models that OHR seems to have any interest in porting to the Western world or any third-party Amazon stores that will grease western influencers with freebies in exchange to dump them on western consumers like we see on YT from time to time.
OHR seems to mainly prioritize the industrial segment.
There are tons of Chinese test devices that we simply don't see here on the western market' so you have to do your homework - some due diligence efforts.. and often you simply cant find info on these foreign items, but there is also a joy in trying out new devices that haven't already been analyzed five ways to Sunday.
I personally like going down these rabbit holes and finding test-devices that I haven't seen before and cant find any user feedback or YT videos, but that's me... I get that many want some assurance, and maybe prefer that other people can vouche or that some social media influencers can guide them, before taking the plunge.
These models from OHR-is jacked with features...and why they have 5 banana sockets, alongside TypeC and USB3-A, that seem to be used for compensation (int/custom/ext) it also came with a small thumbstick, that looks like a USB thumb drive, with a USB-3 interface, and written ext cold junction compensation.
On this "03"-model it also refers to.
Recording function, RS485 function, HART function, TTL function, Bluetooth function, AC measurement..but to what extent.. don't know yet.
Many of these aspects, are optional features where you need to go pretty far up the price ladder on high-end models to acquire, so it's really not apples to apples with these 2 sockets LBxxx models with MicroUSB, which can be had as low as 15$ for some of the variants (LB02G)
![OHR Multifunction Process calibrators [OHR-C03]](https://www.eevblog.com/forum/index.php?action=dlattach;topic=448957.0;attach=2472897;image)
Alongside you have minus, microvolt tolerances down 1uV entry sensitivity, 1A measurement ablelity (if I recall) and also way higher resistance and frequency ability than fx LB02A, and you can program various aspects of these things, and features that seems to be common on the more adv process multifunction signal process calibrators and having waveform ability for both source & measure.. its a pleasure to visualize signals, not least relative fast moving signals or variables over long time.. you can adjust the graph on its acquisition time from 00.1s to 60.0..
Havent seen any menu so far about end-user calibration, but then again I don't have the reference source tools to deliver finer tolerances or even validate some of these specs with any meaningful certainty.
As mentioned it takes quite a few minutes before it finally settles down at 0uV.. it will start at around -6 to 8uV and then slowly center... it takes a long time before it reaches 0uV. like 10 to 20 minutes but could be the norm when dealing with such minute values.