What does this reading mean on a multi meter -0.00

[OnlQQker]

So checking for voltage on a brake light today on a Ford Transit 2016 custom.

The drivers side is ok, the passenger side came up no voltage and gave a reading of -0.00. Multi meter set to 20v DC
When keys are out of ignition the reading was 0.00 without the minus in front of it.
I did try the tips of the multi meter the other way around on the wiring using the chassis as negative but made that made no difference to the -0.00 reading

Trawling through the Ford forums it looks like it was probably a duff bulb and the ECU needs resetting. Looks like one of those annoying things that seem to be happening to Transits and brake bulbs. On the other hand I've have never had a reading of -0.00 before.


Though it's probably nothing I just wondered if anybody might have an explanation for this. I've searched the internet in vain before annoying anybody around here about this, but found zilch.
I thought I'd better ask as I run the risk of no sleep for weeks on end whilst trying to figure out what the minus means.

Thanks in advance!

 

[littlespark]

-0.001 then rounded down. Different to 0.001 which is positive.

Readings that small could be down to anything, such as a dog farting 3 streets away….

Or your multimeter just not being sensitive to detect such a precise reading.

 

[DPG]

A digital multimeter has a high input impedance, and will not always show exactly zero. Even with nothing connected the display may show a slight negative or positive reading - even moving the leads may make it vary slightly.

Only highly accurate and calibrated millivolt meters will be accurate down to the tiny levels that would be needed to show an absolute zero.

Long story short, when testing automotive electrical systems with amultimeter, -0.01V is pretty much the same as +0.01V.

 

[pc1966]

It is almost certainly just a negative value below the least significant digit.

As an aside, there is such as thing as a "negative zero" in common floating point maths in computers, used for handling certain special cases like the error return value from sqrt(-1.0) and similar:

Signed zero - Wikipedia

en.wikipedia.org

 

[OnlQQker]

Thanks very much for taking the time to post everybody.

I've been using the multi meter for a while now and had never seen this reading before.

@pc1966 Signed zero was an interesting read, and has lead me on a new study, thanks for posting the link.
Below is the section of your link which caught my eye!

"The concept of negative zero also has some theoretical applications in statistical mechanics and other disciplines."