anchor.diff:    }
     
     void draw() {
  -    num baseHeading = TAU * (heading / 360);
  +    num baseHeading = getHeadingRad();
       num deltaX = Math.cos(baseHeading);
       num deltaY = Math.sin(baseHeading);
       num newX = x + delta * deltaX;
  
positive.code:   
    void drawFillCircle(ctx, num x_, num y_, num radius, color) {
      ctx.beginPath();
      ctx.setLineWidth(2);
      ctx.setFillColor(color);
      ctx.arc(x_, y_, radius, 0, TAU, false);
      ctx.fill();
    }
  
negative.code:     cleanCtx(turtleCtx);
      if (delta != 0 && penupdown == PENDOWN) {
        userCtx.beginPath();
        userCtx.lineWidth = 2;
        userCtx.fillStyle = BLACK;
        userCtx.strokeStyle  = BLACK;
        userCtx.moveTo(x, y);
        userCtx.lineTo(newX, newY);
        userCtx.stroke();
  