I find that the qty shown in the owner's manual and the actual qty required by the engine can vary slightly. For instance, my 28EFI Lazer manual calls up 2 quarts, but the actual engine only takes 1.8 quarts to the full mark. Here is what I always do with a new machine:
1. drain the old oil and change the filter
2. if the book qty is 2 quarts, put in 1.5 quarts
3. run the engine for a few minutes to move the oil around and fill the filter
4. let it sit for a minute so the oil drains down
5. check the level and top it up slowly until it get to the full mark
6. note exactly how much you used out of the 2 quarts
7. use a paint pen or marker to write the correct amount on the fill cap
Next time you change the oil, there is no guessing, drop the oil and filter, and refill with 1.8 quarts.
I do this for every machine including the vehicles - makes oil changes a snap.