The length of your foot can be used as a standard unit of length.
Why is a foot step,or a handspan, not used as a standard unit of length?
Why can we not use the length of a rod as a standard unit?
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 the above features are not present?