datum vs reckoning

datum

noun
  • A premise from which conclusions are drawn. 

  • A floating reference point, or SLDMB, used to evaluate surface currents in a body of water. Often employed by coastal search and rescue. 

  • A fixed reference point or set of reference points which precisely define a system of measurement or a coordinate system. 

  • A fact known from direct observation. 

verb
  • To provide missing data points by using a mathematical model to extrapolate values that are outside the range of a measuring device. 

reckoning

noun
  • An opinion or judgement. 

  • The working out of consequences or retribution for one's actions. 

  • The action of calculating or estimating something. 

  • A summing up or appraisal. 

  • The settlement of accounts, as between parties. 

How often have the words datum and reckoning occurred in a corpus of books? (source: Google Ngram Viewer )