Groves, Robert (2004). Survey Methodology. New Jersey: Wiley. "By measurement error we mean a departure from the value of the measurement as applied to a sample unit and the value provided. " p 51-52 .
metricationmatters.com
Naughtin, Pat (2007). "What is metrication"(PDF). Pat Naugthin. pp. 4, 5. பார்க்கப்பட்ட நாள் 13 June 2013.
