GMC-300E Geiger counter data logging in C#

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO.Ports;
using System.Text;

namespace SerialPortTest
{
    /* Implementation of GQ-RFC1201 http://www.gqelectronicsllc.com/download/GQ-RFC1201.txt */
    class Program
    {
        static SerialPort port;
        static List<ushort> heartbeats;

        static void Main(string[] args)
        {
            heartbeats = new List<ushort>();

            port = new SerialPort("COM9", 57600, Parity.None, 8, StopBits.One);

            port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);

            port.Open();

            port.WriteLine("<GETVER>>"); // get the device version

            port.WriteLine("<HEARTBEAT1>>"); // enable counts per second heartbeat

            while (true)
            {
                System.Threading.Thread.Sleep(10);
            }
        }



        private static void port_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            var buf = new byte[port.BytesToRead];

            port.Read(buf, 0, buf.Length);

            if (buf.Length == 2) // this is most likely a heartbeat
            {
                Array.Reverse(buf);
                var bits = new System.Collections.BitArray(buf);
                bits[14] = false;
                bits[15] = false; // "The highest bit 15 and bit 14 are reserved data bits."

                bits.CopyTo(buf, 0);
                var outint = (ushort)BitConverter.ToUInt16(buf, 0); // the CPS value as unsigned short
                addHeartBeat(outint);
            }
            else Console.WriteLine(Encoding.ASCII.GetString(buf));
        }



        static void addHeartBeat(ushort source) // keep the last 60 values in a list and compute the CPM value by adding them
        {
            heartbeats.Add(source);

            while (heartbeats.Count > 60) heartbeats.RemoveAt(0);

            int cpm = 0;
            foreach (var hb in heartbeats) cpm += hb;

            Console.WriteLine(cpm + " cpm");
        }
    }
}