Which multimeter are you using?

What does this mean (from the Brymen's spec page):

AC voltage measuring accuracy ±(0,5% + 30 digits)

Specifically, the "+ 30 digits" part?

I believe it is the same as LSB when speaking about ADC or DAC: +/- 30 of what the smallest digit shown on the display represents.

None. Mine broke after I decided to take it apart due to some faulty readings I was getting. The new one is from Banggood and should arrive this week.

I'm still struggling to get my head around it. 30 requires two digits, of course, so is it saying the last two digits displayed are basically nonsense? Why bother with a five or six digit display, in that case?

The Brymen 789 has 5 digits in the display and auto range. If I measure a 1.5V battery, it will display 4 digits after the dot. If I measure mains (230V), it will (only) display two digits after the dot. You can essentially say, the lower the voltage the more digits after the dot you will get.

A friend of mine works professionally as an electrician. He has (through his job) a Fluke DMM (do not know the actual model, it is a rugged one), and when comparing the measurements of a 1.5V AA battery, the difference between the two is 0.0003 volts. Measuring a 10K resistor gave same result. Not tried with a capacitor but I believe it would also be very close.

You didn't have a 2nd meter to help you understand what was going on with the first?

Yes, I did take a look at the specs, and it's an impressive meter. I just didn't understand the '30 digits' part. Still don't.

Good point. You don't have just one meter! :sunglasses:

Hank Hill WD-40
Gotta have tools to work on your tools

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I know how it died.

I kept forgetting to switch the settings and also didn't know how to measure amperage properly. Ended up just shorting and only the volts setting worked.

I just took a new meter out of its packaging.

I have to add my list:
In the spare room with my ham radio equipment is a BK toolkit 2703A that was part of a test set for a former product of a former customer.
In the garage, A Beckman tech300 that I bought in 1980 when I began my data communication consulting business.
In my shop, an unknown DVM identified as MY-6Y. My former business had dozens of excess DVM, so I selected one for home use.
Also in the shop is a Simpson 260 that I was issued in the 1970's by Airforce MARS, a military amateur radio affiliate organization.
All get used when necessary and all still work.

Our engineering class in my middle school is in a workshop, and just outside is an old auto body shop. Me and my friends took a poke around and found a Hitachi V209 oscilloscope.

For an idea of how old this thing is compared to something from Keysight or another company, here's the user manual:

V-209-Oszilloskop_Operation_Manual.pdf (2.5 MB)

It also uses a CRT as it's display. Because yes.

To be honest, neither do I. Maybe the claim is that the DMM uses 30 digits internally which is then rounded to fit into the 5 digit display. That would be quite impressive (and probably unnecessary), though!

Fluke 87V, and a few of them at work.

A benchtop Keysight model 34470A DMM, for calibration certification. (NATA Certified)

In 10years of doing cal/certs never had to fail a Fluke, except one that got run over. :sleepy:

Yet the Keysight failed its cal in first 12month checkup, replaced under warranty.

My first Fluke was model 77.

Nice bit of gear, someone else thought so to, only had it 6 months.

Tom... :grinning: :+1: :coffee: :australia:

Thank you for your answers. I continue to read them carefully and I will make my choice soon.

Forgot about this topic.. I am pretty sure that I figured out the "+ XX digit" stuff from product-bragging. Lets look at some A/C true RMS precision claims:

6V +/-(0.5% + 30 digit): 0.5% from 6V is 0.03V and 30 digits in a display with 4 decimals is 0.003V, so the accuracy must be +/-0.033V.

1000V +/-(0.5% + 30 digit): 0.5% from 1000V is 5V and 30 digits in a display with 1 decimal is 3V, so the accuracy must be +/-8V.

I would like to be corrected if I'm wrong about this.

EDIT: Calculatory brain fart.

I have a several multimeters of varying quality both digital and analog. The one I use the most frequently though is a Siglent SDM3045X. Not a high end multimeter but not a slouch either, it's a pretty good value in my opinion. The ability to dump readings into a file on a USB drive is pretty handy.

Hi, @Danois90 @SteveThackery
I find the DC specs are this, so it does cast doubt over the other specs

These are more than reasonable.


This link might help, the high digits is due to the many digits it can display.

If you want to see your DMM performance try this guy on YouTube.

Tom... :grinning: :+1: :coffee: :australia:
PS. I wonder about DMMs that have these fantastic digital resolution, then tell you the last digit can be 30 to 70 counts out.
When you analyze the accuracy you can throw out the last 1 or 2 digits anyway.


Thanks, @TomGeorge, that's very interesting.