See "in common circulation". Neither the half-penny nor the paisa are in common circulation, neither physically nor digitally. Case closed. You are the one who brought physical length into the discussion, and we need physics for length. Both a meter and an angstrom can be expressed in terms of the Planck length. There is no other "base unit" for length. To say one meter is some kind of official global base unit for length is goofy. It's just a unit some people picked to compare to in some situations, and any other unit can also be compared to. Bitcoin's 21 million bitcoin is completely arbitrary, decided by humans. Last time I checked humans didn't have all that much into into the speed of light, but hey, I wasn't in the room.