Example of using non-linear math with noUiSlider

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<link rel="stylesheet" href="http://refreshless.com/nouislider/source/jquery.nouislider.css">
<script src="http://refreshless.com/nouislider/source/jquery.nouislider.js"></script>
<div class="slider"></div>
<span></span>

CSS

#slider {
    margin: 40px;
}

JavaScript

// https://gist.github.com/maccesch/995144
var Lagrange=function(x1,y1,x2,y2){this.xs=[x1,x2];this.ys=[y1,y2];this.ws=[];this._updateWeights()};Lagrange.prototype.addPoint=function(x,y){this.xs.push(x);this.ys.push(y);this._updateWeights();return this.xs.length-1};Lagrange.prototype.changePoint=function(index,x,y){this.xs[index]=x;this.ys[index]=y;this._updateWeights()};Lagrange.prototype._updateWeights=function(){var k=this.xs.length;var w;for(var j=0;j<k;++j){w=1;for(var i=0;i<k;++i)if(i!=j)w*=this.xs[j]-this.xs[i];this.ws[j]=1/w}};
Lagrange.prototype.valueOf=function(x){var a=0;var b=0;var c=0;for(var j=0;j<this.xs.length;++j)if(x!=this.xs[j]){a=this.ws[j]/(x-this.xs[j]);b+=a*this.ys[j];c+=a}else return this.ys[j];return b/c};

var l = new Lagrange(0, 0, 100, 200000);
l.addPoint(20, 10000);
l.addPoint(75, 100000);

$.fn.writeLagrange = function(a){
   this.text(l.valueOf(a));    
};

$(".slider").noUiSlider({
    range: [0, 100],
    start: 0,
    handles: 1,
    serialization: {
        to: [$('span'), 'writeLagrange']
    }
});