assess vs gradate

assess

verb
  • To determine, estimate or judge the value of; to evaluate 

  • To impose or charge, especially as punishment for an infraction. 

  • To calculate and demand (the tax money due) from a person or entity. 

gradate

verb
  • To arrange in order of grades. 

  • To change imperceptibly from one gradation of tone etc. to another. 

  • To bring to a certain strength or grade of concentration. 

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