Mehemea e inea ana te rahi o tētahi mea ki te āwhata motukore, e kore e tōtika pū te ine. Mēnā ka kīia ko te 21cm te roa o tētahi mea, ko te tikanga e pātata atu ana ki te 21cm, tērā i te 20cm, i te 22cm rānei. Ko te pae hapa kei waenganui i te 20.5cm me te 21.5cm.
If something is being measured against a continuous scale, the measurement will never be exact. If something is said to be 21cm long, this indicates that the length is closer to 21cm than 20cm or 22cm. The margin of error is between 20.5cm and 21.5cm.