Newbie at reading serial data from LRF

I'm currently using an Opti-Logic RS400 Laser Range Finder along with an Arduino MEGA 2560 for a project. I've been trying to read the serial data using code I've found online, but what I get back is gibberish because I don't know how to properly filter or convert the data. I've tried using simple serial reading code like this:

String readString;

void setup() {
      Serial.begin(9600);
      Serial2.begin(19200);
      Serial.println("Serial Test");
        }

void loop() {

      while (Serial2.available()) {
        delay(100);  
        if (Serial2.available() >0) {
          readString = Serial2.read();
          readString += c;}
      }
        
      if (readString.length() >0) {
      Serial.println(readString);
      
      readString="";
      } 
   }

However, this is what I receive in the serial monitor:

Serial Test
?}-¥g!1-9¿[Y???¿[=#153-#75e¿S5e?£?åë'!5¿?¿

When I need to receive something like:

Serial Test
DIST:0046.61F
DIST:0046.42F
DIST:0046.25F

The lrf uses RS-232 serial, and I thought this data could be readily converted with Arduino into string form, but I must be missing several steps. I set the Baud rate to 19200 which is under the specs, but the sensor is a little odd in that the instructions ask me to use HyperTerminal in Windows with specific settings to operate it through Windows. What vital step am I missing?

RS232 uses different logic levels than TTL Serial. You need a conversion, like the MAX232 chip. Google it.

So all the serial input/outputs on the Arduino are default TTL serial? Thanks, hopefully this will give me some readable data.

I also had some sensors that might be 3.3V(?), do I need some kind of converters to make them 5V even though they're TTL? Sorry if messed up some of the jargon, I'm extremely new to this.

3.3V is sometimes called LVTTL (Low Voltage TTL). If you are talking Serial signals you are in luck. since 3.3V is well above the minimum required for a TTL '1' signal. You can safely connect a 3.3V TTL output to a 5V TTL input. The other way around depends on if your 3.3V input is "5V Tolerant". If not, you can use a voltage divider to bring the 5V signal down to 3.3V:

5V Output ----////-----3.3V Input-----////----Ground
10K 20K

Thanks again for the advice. I picked up an RS232 shifter, and I'm finally receiving the correct data on my computer. Wish I could upvote you for the help; saved me from experiencing a lot of headaches.