The chain or tape being used may not be the correct length so it may always over or under read (a systematic error). This can be corrected by:

L = l x actual tape length
assumed tape length

For example:

l = 226.20
assumed tape length = 30.00 m
actual tape length = 30.005 m

then:

A tape is standardized by comparison with a "standard" tape or by measuring a definite "known" distance.