public static String lenghtUnitIndexToString(int index) {
        switch (index) {
            case 0:
                return "m";
            case 1:
                return "ft";
            case 2: 
                return "mm";
            case 3:
                return "cm";
            case 4:
                return "km";
            case 5:
                return "mi";
            case 6:
                return "in";
            default:
                return "m";
        }
    }