This piano was more than a half step flat! Tuning something this poorly maintained is not much fun, but the task is made much easier by an ETD (Electronic Tuning Device). If you watch the display carefully, you can see, as well as hear, each of the three strings rise in pitch until they are all at the target pitch. Customers often ask about the difference between tuning by ear (aurally) vs. using an electronic device. Some people hold to strong positions one way or the other. At the end of the day, the quality of the tuning is what matters! I use both methods, but I tend toward mostly aural for fine tuning quality instruments, and mostly electronic for a first-pass pitch raise like this, where all you can expect is to get it in the ballpark.
Pianos do not naturally go out of tune this badly! For a single note on a piano to be this wild, it is highly likely that a previous owner tampered with the tuning pins in some way, perhaps in a less-than-successful tuning attempt. It would not be the first time I’ve run across that… I don’t ever discourage people from working on their own piano – in fact, I think it’s a good thing. Just make sure you do your research first and know what you’re getting in to! Suffice it to say it’s more complicated than it appears. A very out-of-tune piano