I am a sight judger sometimes too. But of course exact measurements is the best way, and tends to allow more consistency. For the OCLT testing especially you will need to be very precise (and know exactly where your level is after the add is done), so we can monitor the exact overnight loss, but otherwise if it's 3quarts, and 3 cups and you want to use the full gallon that's fine, just retest 30 mins after to see where you end up It's most important to keep it at or slightly above the shock level at all times. (the main goal is to not let it drop below shock level ever, but too high of levels isn't good for your pool, and equipment. But it appears by the numbers that he's doing great.
EDIT: Pool math is very accurate, so if your numbers have been rising to the expected level, which they have, then there is no need to recheck after every single time since you are checking so frequently anyway, EXCEPT when doing OCLT, and then you need to ensure you know exactly where it is at.