potjie vs slow cooker

potjie

noun
  • A lidded round-bottomed pot used for cooking in South Africa. 

slow cooker

noun
  • A kitchen appliance consisting of a clay pot and its housing with self-contained electrical heating, characterized by a loose-fitting lid, relatively low temperatures, and long cooking times, and used especially in the preparation of stews. 

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