def compute_pwp(clay_val, oc_val, sand_val):
    """
    Calculate permanent wilting point based on Clay, Organic Matter and sand value
    :param clay_val: percentage of clay
    :param oc_val: percentage of organic carbon
    :param sand_val: percentage of sand
    :return: a float value representing PWP
    """
    om_val = 2 * oc_val
    om_val /= 1000
    clay_val /= 100
    sand_val /= 100
    theta_1500_t = (0.031 - 0.024 * sand_val + 0.487 * clay_val + 0.006 *
        om_val + 0.005 * sand_val * om_val - 0.013 * clay_val * om_val + 
        0.068 * sand_val * clay_val)
    theta_1500 = 1.14 * theta_1500_t - 0.02
    return round(theta_1500, 2)
