The number is not the mark
A lab that produced 8.2 where the book says 9.8 loses nothing at all, provided the report says why. A lab that produced 9.8 and cannot account for itself loses more than people expect.
Error analysis carries it
Named sources, the direction of the effect, and a rough magnitude. *We probably lost mass to the filter paper, which pushes the yield down* is worth more than three decimal places and takes a sentence.
The reasoning between the numbers
Every table needs a sentence saying what it shows. Graders mark the sentence. A report that is a set of tables with captions is a report that has left its marks on the bench.
Written after, not during
The report is not a transcript of the afternoon. Do the lab, work out what happened, then write — in that order, and preferably not the same evening.