How does the progress bar work?

[Shooter3k]

How does the progress bar work? I've noticed when I add a new drive to the index, the progress bar basically always only shows 97% or 98% for the duration of the entire scan (which might take hours). Not really complaining, mostly just trying to understand how it works since there's really no way for it to know how much it has to index....since that's literally what it's doing.

It also seems to show (only) 98% or 99% when doing the follow up steps after the drive scan (like "sorting file names")....which also seems odd.

Thanks

[void]

It shows the completed "steps".

Each volume is a "step".
There's one extra step for sorting.