beat off vs jack off

beat off

verb
  • To masturbate, usually a man of himself. 

  • To waste time. 

  • To drive something away with blows or military force. 

jack off

verb
  • To masturbate. 

  • To stimulate or please oneself in an unproductive or idle way. 

  • To manually stimulate someone sexually, generally a male. 

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