I have a chart with tooltip There I display the date and price of the current point.

    var toolTipWidth = 125;
    var width = 600;
    var toolTip = document.createElement('div');
    toolTip.className = 'tooltip';
    chartContainer.appendChild(toolTip);

    chart.subscribeCrosshairMove(function(param) {
      if (!param.time || param.point.x < 0 || param.point.x > width || param.point.y < 0 || param.point.y > height) {
        toolTip.style.display = 'none';
        return;
      }

      let price = param.seriesPrices.get(areaSeries);    
      let date = LightweightCharts.isBusinessDay(param.time) ? businessDayToString(param.time) : new Date(param.time * 1000).toLocaleDateString();

      toolTip.innerHTML = `<div class="tooltip__price">${price}</div><div class="tooltip__time">${date}</div>`;
      let left = param.point.x - toolTipWidth / 2;
      left = Math.max(0, Math.min(width - toolTipWidth, left));

      toolTip.style.left = left + 'px';
  });

On the chart, I need to show the dynamics of growth (how much the amount has changed, whether there has been an increase or decrease, how much it is as a percentage). To do this, I need to get the previous point and compare it with the current one. But only one chart point is passed to the tooltip function. How to get the previous value?