In general, I don’t think trying to figure out why a certain preposition is used is going to be very productive. But in this particular case, the use of “off” does reflect “away”. Mark off every two inches. That’s where we will drill holes. (Place a mark two inches away from the previous mark) Measure off 50 paces. (Find the place 50 paces (steps) away from here) Your other example “off your hand” isn’t correct. Maybe you mean “keep your hands off!” (Keep your hands away)

@Mario Thank you so much :D

Off is a prepostion. All prepositions will depend on a verb, the verb will determine the meaning of the verb. Learning the meaning of every preposition makes little sense since the use of prepositions between languages is highly arbitrary. I would suggest learning verbs together with the prepositions that can be used with a specific verb, that will give you a more accurate idea of what the preposition means with every verb.