Nah all joking aside. Cookie is quite right the scal & units dont matter could well be tomatoes or troy lbs. Just keep the point you are setting up from constant. If you change the constant you go back & start again.
It is so individual & no 2 boats would be set the same

All points taken onboard.. The idea was to mark the "so called datums" as zero and then plus and minus from there (with a big mark/marks at the "sweet point/points") so at least she has some kind of understanding of how high or how trimmed the motor is rather than just a numbered scale which i agree dosen't really mean anything