above-board vs understandable

above-board

adj
  • In open sight; without trick, concealment, or deception. 

adv
  • Honestly; openly. 

understandable

adj
  • Capable of being understood; comprehensible. 

  • Capable of being accepted or excused under the circumstances. 

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