Understanding the progress bar and outputs from get_standard_metrics()

[Serendipity31]

I have some questions and a suggestion related to the progress bar and its documentation

Question:

Can anyone help me to understand what the default progress bar output in Lightning 2.1.0 shows?

I'm struggling to understand what the progress bar is showing me. Below is one example of what I see in my use case (note that the example below is the result of just leaving the default progress bar and logging behaviours unchanged during training):

Epoch 6: |     | 50/? [00:05<00:00,  9.31it/s, v_num=47, train_loss=1.280]

When I see this on my console, it raises questions. For example:

• Why is there an empty gap in between the '| |' above? I presume this is where the bar is supposed to show, but bar ever appears there.
• What does the number 50 represent, and is that a number I should proactively set?
• Is it a problem that '50' seems to have an undeifned range/max (as indicated by the '?' in '50/?' part of the progress bar output)?
• What time is being shown in '00:05<00:00', and does that make sense that a non-zero time is 'less than' zero time, or does this indicate something isn't working?
• Can I re-set v_num if I want to, and if so, how does one do that? It seems to keep counting up across days of trying out different settings.

Suggestion

I think it would be really constructive if the documentation on this could be expanded and made more explicit. This is a point that has been raised in a closed thread here, but I think it's still a gap.

The documentation does mention that the 'version number of the experiment' is shown by default. This explains what v_num stands for in the progress bar, but not what governs its behaviour.

However, the only place I find any additional information on the outputs is in the comments within the source code for the definition of get_standard_metrics(). Even that doesn't fully explain the progress bar outputs that I'm seeing. Maybe it's somehow self-evident to advanced users, but as a new user I've spent quite some time looking for this information in the documentation (and other relevant fora online where people post questions), expecting it to be fairly straight forward to find, and I haven't managed to find the answers to these questions.

If the information is there, maybe it's just a case of signposting it a bit differently to help new users find it more easily. If it's not there, perhaps one well sign-posted and elaborated example showing how to 'read' the output could be enough.