Here is an overview and comparison of my three DMMs.
Left to right they are a Beckman Tech 310, Digimess DM200 and BSide ZT102. 
I recently purchased a 2.5000V .01% reference from Doug Malone. I will use that to compare DC accuracy at a single point. Best I can do with my home gear.
Beckman Tech 310
Beckman Instruments, now Beckman Coulter, is an American manufacturer of Biomedical Instrumentation. In the early 1980s Beckman made a series of high quality hand held DMMs. A few years later San Diego based Wavetek took over Beckman’s DMM line and it disappeared. I bought mine around 1982. At the time analog meters were still common.
This manual ranging meter is easy to use. The large selector knob has positive detents and a quality feel. Measurements are quick, perhaps because the meter isn’t auto ranging and is 1999 count.
The meter is exceptionally durable. It survived significant voltage on the resistance settings. I’ve dropped it many times and it keeps on working. I still use it regularly. Even the original test leads are still good.I’ve never had the meter calibrated. After 35 years it is still in spec and only 1 count off!
Single Ceramic fuse accessible from the battery compartment. The Tech 310 pre-dates Cat I, II, III, and IV ratings. I dunno. It is pretty well made and held up fine measuring high voltages. I’ve used the 1500VDC and 1000VAC scales before. I’m not sure if I would risk it now. Any capacitors in the meter are getting really old.
Removing the back cover reveals a large shield.
There are two circuit boards full of 1980’s tech. Note the single potentiometer just to the left of the top board. That sets DC calibration. By some amazing coincidence 2.50V is the set point 
After a slight adjustment.
