It's a time record and an important diary.
The time record never exists in isolation.
With a little expansion, he could have spawned another product, such as an "important diary".
We go to the "month" data table, sift through the current month's data, descend it, find the single longest lasting activity, and then recall what we were doing at the time, adding "notes". While memories are certainly not immediately accurate, it's better than nothing.
After you've added the notes, create a new column with "important things" at the head of the table, then add a star (★ or something else) for those things that you think are important to you, and refresh the "monthly perspective" table.
The quality of the time period can be judged by the "number of important things" in the time period, the more "★" means the higher the quality.
The final push back to the year, resulting in a yearly list of big accomplishments that become your life record book.