Example of error:

A survey line AB was measured by a chain of 30 m length and was found to be 2340 m. The similar line AB when measured by a 20 m chain, the length was recorded as 2350 m. While calibrating the 30 m chain was found to be 2 cm too short. What was the error in 20 m chain?

Solution

Actual length of 30 m chain = 30.0 - 0.02 = 29.98 m

True length of AB =L′/L × Measured Length

= 29.98/30.0 × 2340

= 2338.44 m

When AB was measured by 20 m chain.

True length =L′/L× Measured Length

2338.44  =L′ /20× 2350

L′ = 2338.44 × 20/2350 = 19.902 m

≈ 19.90 m

Hence, the incorrect actual length of 20 m chain is 19.90 m, i.e. 10 cm too short.