What does "Log today" do?

Creates today's row and takes you to it, so you can type in the columns the app cannot work out for itself.

Log today sits at the right-hand end of every daily-log row on the desk. It does two things in order: makes sure today's row exists, and drops you on the Data tab with that row's check-in strip at the top.

What the strip shows depends on the dataset. The computed columns for today are printed as plain values — you are not editing those, you are reading what the bars said. The manual columns are shown as editable controls: a dropdown for a category, Yes/No for a boolean, a box for a number or a note.

If the dataset has computed columns and an instrument, pressing Log today first fetches today's bar. On a day the market has not closed yet — or on a holiday — there is no bar to fetch, so it creates a blank row for you to log into anyway.

You cannot end up with two rows for the same day by pressing it twice; the button guards against that, and against a backfill that is still running underneath.