building-rotavo-13.html

<input-knob value="2.5"></input-knob>
<input type="range" name="angle" min="0" max="6.28" step="0.1" value="1" />
<script>
  const knob = document.querySelector('input-knob');
  const slider = document.querySelector('input[type=range]');
  // Just take the value from the slider and set it straight on the knob
  slider.addEventListener('input', () => { knob.value = slider.value; });
</script>