call of duty vs registration

call of duty

noun
  • What one's duty obliges one to do. 

registration

noun
  • The act of signing up or registering for something. 

  • The art of selecting and combining the stops or registers of an organ. 

  • That which registers or makes something official, e.g. the form or paper that registers. 

  • Alignment, e.g. of colors or other elements in a printing process. 

  • The location where guests register, especially with a hotel. 

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