C#

private string ScaleRtf(string text, double scale) {
	log(text);
	int lastPosition=-1;
	for (; ; ) {
		int i=text.IndexOf(@"\fs", lastPosition+1);
		if (i<0) break;
		lastPosition=i;
		log("Found fs at "+i);
		int fs=0;

		for (i+=3; ; i++) {
			char c=text[i];
			int j="0123456789".IndexOf(c);
			if (j<0) break;
			fs=10*fs+j;
		}
		int newFs=ScaleUp(fs, scale);
		text=text.Substring(0, lastPosition)+@"\fs"+newFs.ToString()+text.Substring(i);
		log(text);
	}
	return text;
}

private int ScaleUp(int fs, double scale) {
	return (int)(fs*scale+0.5);
}

private void log(string s) { }

using System;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        System.Timers.Timer timer;
        public Form1()
        {
            InitializeComponent();
            timer = new System.Timers.Timer();
            timer.Elapsed += new System.Timers.ElapsedEventHandler(timer_Elapsed);
            timer.Start();
        }

        void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            /* System.InvalidOperationException "Cross-thread operation not valid..."
            will be thrown if you try to alter the property directly from a different thread */
            if (this.InvokeRequired)
            {
                BeginInvoke(new MethodInvoker(delegate() { UpdateText(sender, e); }));
            }
            else
            {
                UpdateText(sender, e);
            }
        }
        private void UpdateText(object sender, System.Timers.ElapsedEventArgs e)
        {
            Text = e.SignalTime.ToString();
        }
    }
}