plus sign vs strength

plus sign

noun
  • The symbol + used to denote the operation of addition, to indicate that a number is positive, and so on. 

strength

noun
  • A positive attribute. 

  • The intensity of a force or power; potency. 

  • The quality or degree of being strong. 

  • The strongest part of something; that on which confidence or reliance is based. 

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