double Dutch vs understandable

double Dutch

noun
  • A game of jump rope with two ropes and frequently two jumpers. 

  • A language game akin to pig Latin. 

  • Incomprehensible language. 

  • Sex using a condom and the contraceptive pill at the same time. 

understandable

adj
  • Capable of being accepted or excused under the circumstances. 

  • Capable of being understood; comprehensible. 

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