In ancient India, small length measurements used were an 'angul' (finger) or a mutthi (fist). These methods were stopped because of the need for a standard unit.
Size of the body parts varies from human to human.
Everyone's body parts could be of slightly different sizes. This must have caused confusion in measurement. The world needed a standard system of measurement. For example, 1 kg of rice in India should weigh 1 kg in Europe as well.