Greatest Possible Error

Question

A man's waist measures 90 cm. What is the greatest possible error for the measurement?

Can someone help me work through this problem?

Answer 1

If no other information is given, assume there is an uncertainty of ±1 in the right-most digit. In this problem, a measurement recorded as 90 cm really means the actual value is between 89 and 91 cm. If the measurement had been recorded as 90.0 cm, then the actual value is between 89.9 and 90.1 cm.