const uint8_t MN00[] PROGMEM = "Menu/exit";

const uint8_t MN10[] PROGMEM = "RTC Setup";
const uint8_t MN20[] PROGMEM = "Card Setup";

const uint8_t MN11[] PROGMEM = "Time";
const uint8_t MN12[] PROGMEM = "Date";

const uint8_t MN21[] PROGMEM = "Mount";
const uint8_t MN22[] PROGMEM = "Umount";

const uint8_t *MENU[] = { MN00, MN10, MN20 };

(uint16_t)MENU[0]

uint8_t MenuStrSize(uint8_t idx) {
    uint8_t size=0;

    while (pgm_read_byte((uint16_t)MENU[idx]+size) != 0) {
   size++;
    }

    return size+1;
}