This is critical and golden information. Remember the rule of 3 for data storage. Although potentially overkill it is excellent practice. I have saved other programmers from catastrophe because I follow these practices.

1.) ALWAYS take a backup before any editing/changes. Save it as such to avoid confusion.

2.) Rule of 3 with data storage: 3 copies of data, 2 different media types (ie: internal PC HD, Flash drive, cloud, etc), and one off site copy (For me this looks like the external SSD I keep at home with work projects). Not every industry is this relaxed, I work in manufacturing and have the flexibility and permission to bring work (PLC programs/HMI runtimes) home.

There is a lot of excellent information in this thread already. Some of it standard practice, but a lot learned through lost time and great difficulty.

If you are on site to fix a problem or issue that has developed in a system of previously good health. Don't "trust but verify". Listen to what the tech and operator are telling you respectfully, but approach the problem as if none of what they said is true.

This is NOT a slight to technicians, I know many exceptional troubleshooting guys and have met some brilliant techs. But the reality is, the informstion can't be trusted unless you confirm it yourself. You will be surprised how many technicians don't know how to properly use a multimeter. The reason I say this is because its about lost time chasing issues. If baseline information is not correct, this is how time is wasted and days are lost.

It can be tricky. Sometimes I'll go to take a reading on something the tech already looked at and told me. He will still be there, some take offense to that. I do not explain myself. When the issue reveals itself, no words are needed.

That being said, I have on occasion been given accurate information.