I haven't understand Jasmine.clock().tick() in jasmine

I have started to learn Jasmine because I have to use it in my new Job, but actually I faced problem with understanding clock().tick().

I copied the following spec from jasmine official documentation, actually I don't understand why in the second tick is used 50 instead of 101. Can you explain me why ?

  it("causes an interval to be called synchronously", function() {
    setInterval(function() {
      timerCallback();
    }, 100);

    expect(timerCallback).not.toHaveBeenCalled();

    jasmine.clock().tick(101);
    expect(timerCallback.calls.count()).toEqual(1);

    jasmine.clock().tick(50);
    expect(timerCallback.calls.count()).toEqual(1);

    jasmine.clock().tick(50);
    expect(timerCallback.calls.count()).toEqual(2);
  });