One of the lesser attributes of digital scopes vs analog is that there are numerous menus to wade through to see setups, whereas with analog scopes the entire setup is immediately visible by visually scanning the knobs and switches. Just today I was getting very strange results until I finally clued in that I had left one channel on AC coupled from yesterday, a mode I very seldom use. Yeah, I felt pretty darn silly for overlooking this basic setup.
We've all done it, so don't feel bad. With power comes complexity. Many of the newer scopes have customization capabilities, so you can save your frequenctly used setups. I do that also for demo's. If anything can go wrong, it will always occur at a live demo.
One of the First things I do when working with scopes is hit the Default Setup button. I have learned from my colleague test engineers spending hours tracking down problems that are due to scope setup rather than DUT output. ALWAYS run a Default Setup (and a front-end cal, if available).
again, these are good points. Most oscilloscopes today allow you to store machijne setups. I save my popular ones and can then recall a particular setup rather than the default. This is also a great idea for demonstrations, where everything seems to go wrong. Having the stored setup is often a relief.