Retained Size in Chrome devTools memory tab

I have attached three different variables to window Object. But why devTools show same retained size for them?

  let a = 23;

  let b = {
    'a': 1,
    'b': 2,
    'c': 3
  };

  let c = () => {
    console.log('I am a simple function')
  };
  
  Window.myNnum = a;
  Window.myObj = b;
  Window.myFunc = c;

Result: They all have 20 Bytes in Retained-Size and Shallow-Size, as below picture: