docs: function( dt ){
  
              if ( dt ){
  
                  this._dt = +dt.toPrecision(4); // only keep 4 decimal places of precision otherwise we get rounding errors
                  // calculate the maximum jump in time over which to do iterations
                  this._maxJump = dt * this.options.maxIPF;
  
                  return this;
              }
  
              return this._dt;
          }