To zero or not to zero

Hello all-

I have heard people say that it is best to zero your DMM when making measurements. I have also heard that it really does not matter if to zero your DMM. So, I guess what I'm asking is which one is correct, or does it depend on the circuit your testing? I'm not too experienced, so I figured you guys can clarify- Thanks

In my opinion, you can never go wrong by zeroing. However, whether or not you NEED to, depends on the application, and how precise your readings must be.

It depends on what you are trying to do. If I'm trying to measure a very low resistance I'll zero the meter to account for the resistance of the meter leads. The leads are usually only about 0.4ohms or less so for 99.999% of resistance measurements it makes no difference.

When measuring voltage if you short your leads together you should read zero volts, if you don't something is wrong with your meter. The only reason to zero the meter would be so account for some small background voltage and then you could easily lead your self astray if for example you are measuring 0.75V between the block ground and battery negative with engine running it would be better, IMHO, to wonder why the block ground has such a high voltage drop then to zero it out to measure a sensor output.

When measuring current with a clamp on meter you will need to zero it as they will pick up noise from current sources other than what you are trying to measure and you want your current measurement relative to the background noise.

That makes since Chad-

I bought the book that Paul put out and there is stuff in it that I never knew about. Many things Im trying to understand and I have a decent older Fluke 23 meter that Im poking around with. I would eventually like to get something like a Snap On vantage eventually, but Im in no rush since I dont do this for money, just more for knowledge. Here is another quick question- I noticed in one of Pauls videos when he was checking the ground side of the TPS and said the power at ground should be no more than 0.1V. Is that just for OCM grounds or the same for all grounds? I guess I need to check my grounds on my truck because at first I got the red lightning bolt and was a parts changer and changed out the throttle body, but now it throws codes for the TPS, IAT, MAP and CKP which I believe all share the same 5V ref and ground. Im using a cheap scanner, but the scanner seems fine.

Thanks for the info Jeff-

This is a learning process and Im starting to write up reference sheets to have in a binder because my memory is shot-

The two things you have to check for is low batteries in your meter which strange as it may seem can lead to high readings and blown meter fuses when measuring current.

Always best to do a sanity on volts scale checking before using the meter, a quick check on voltage across the battery is all that is required.
If you want to be very precise you can test against a precision voltage source. I bought one on eBay years ago very cheaply but the price has risen but still $20/£18/20e range .

Andy.MacFadyen wrote:

The two things you have to check for is low batteries in your meter which strange as it may seem can lead to high readings and blown meter fuses when measuring current.

Very good advice! I still have a voltage regulator on hand that I replaced because I was reading a high charging voltage due to a low battery in my meter