Characteristics of standard/physical units are:
(1) it must be easily accessible
(2) it must be accepted internationally/worldwide
(3) it should be accurate.
(4) it should not be effected by physical conditions like temperature,pressure etc.
(5) its value should neither be too small nor too big.
(6) it should be easy to use.
(7) it should be indistructible and remain in use for long period of time
