double 计算出错

        double pvv = Convert.ToDouble("593");
        double pt1 = pvv * 0.02;           double pt2 = pvv * 0.05;
        double pt3 = pvv * 0.04;
        double pt4 = pvv * 0.03;
        double pt5 = pvv * 0.02;在中断查看 pt2的结果是29.65000000000000002
请问为什么这样，因为这样的原因搞很下面的计算都不精确double 计算出错