Date, place, and one observation, which takes about twenty seconds
The format
Date, where, and one thing noticed. Twenty seconds, standing at the back door, and no requirement that it be interesting.
Why one line
Because it survives busy weeks. A diary that demands a paragraph is abandoned in February; one that demands a line is still going in year five.
What it becomes
After three years you can see the first swifts arriving earlier, or the frogs spawning later. That pattern is invisible from memory alone.
