A standard unit of volume

The standard unit of value, used as medium of exchange during the Vedic period, was :

The standard unit of measuring pressure is

Why can a pace or a footstep not be used as a standard unit of length?

It is desirable that the standards of units be easily available, invariable, indestructible and easily reproducible. If we use foot of a person as a standard unit of length, which of theabove features are present and which are not?