It is measurable in that you can show it and somehow "count" it. Compare with a day if you just discussed back and forth what you should do or how to do it. If there is nothing concrete to show for it, it is not measurable. At least take notes in that case.
Productivity: every day do at least one measurable thing that puts forward your project, even if very small.
But a bit confused on the "measurable" piece, if you write code, make a new feature or fix a bug, how can it be measurable?