Depends on how rich you are
if you are very rich, use meters (or yards)
if you are kinda rich, use feet
if you are average, use centimeters (or inches)
if poor, use milimeters
So
lets say we have
a/b=2a/2b
we know that if we invert one and multiply it by the other (divide them), we get 1 because a/a=1 where a=a
so
2/3 and 4/6 are equivelent because if you divide them we get 12/12=1
2/3 and 8/12 are equivilent because if you divide them we get 24/24=1
and sinde 2/3=4/6 and 2/3=8/12, 2/3=4/6=8/12
they are equivlent