backflow vs depreciation

backflow

verb
  • To flow in the wrong or backward direction. 

noun
  • The flow of a fluid (through a pipe etc.) in a direction opposite to that which is normal or intended. 

depreciation

noun
  • The decline in value of assets. 

  • The state of being depreciated; disparagement. 

  • The measurement of the decline in value of assets. Not to be confused with impairment, which is the measurement of the unplanned, extraordinary decline in value of assets. 

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