Ember importing value and compute function

I have range with currentValue displayed in span. I'm trying to import this value to compute function, make a calculation and return back. I stacked in compute.

range.hbs

<input
type="range"
onchange=
class="form-control"
value=""
min="1"
max="99"
/>

<span class="tag tag-pill tag-info">
   % - %
</span>

range.js

export default FormComponent.extend({

deltaValue: computed('currentValue', function() {
    var newValue = 100 - this.get('currentValue');  
    return newValue;
  })
});