Arduino Timer

static int timer1 = 0, timer2 = 0;
static unsigned long lastmillis = 0;
int i, j;
String command;


void setup() {
  Serial.begin(9600);
}

void loop() {
  unsigned long deltamillis = 0;
  unsigned long thismillis = millis();
  if (thismillis != lastmillis) {
    deltamillis = thismillis - lastmillis;
    lastmillis = thismillis;
  }

  timer1 -= deltamillis;
  if (timer1 <= 0) {
    timer1 += 1; //counting every 1 ms
    i++;
  }

  timer2 -= deltamillis;
  if (timer2 <= 0) {
    timer2 += 1000; //counting every 1000 ms
    j++;
    Serial.print(j);
    Serial.print(" ");
    Serial.println(command);
  }

  switch (i) {
    case 1000:
      command = "Baca Sensor 1";
      break;

    case 2000:
      command = "Baca Sensor 2";
      break;

    case 3000:
      command = "Baca Sensor 1 & Sensor 2";
      break;

    case 4000:
      i = 0;
      command = "";
      break;

    default:
      break;
  }
}