diff -N ClockSingleton.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ClockSingleton.java	29 Aug 2011 23:03:20 -0000	1.1
@@ -0,0 +1,43 @@

+/*
+ * To change this template, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package org.lcsim.hps.util;
+
+/**
+ * singleton clock class - use ClockDriver to control.
+ * A better solution might be to store event number/absolute time in the event.
+ * 
+ * @author Sho Uemura <[log in to unmask]>
+ * @version $Id: ClockSingleton.java,v 1.1 2011/08/29 23:03:20 meeg Exp $
+ */
+public class ClockSingleton {
+    public static final ClockSingleton _instance = new ClockSingleton();
+
+    private int clock = 0;
+    //time between events (bunch spacing)
+    private double dt = 2.0;
+
+    private ClockSingleton() {
+    }
+
+    public static int getClock() {
+        return _instance.clock;
+    }
+
+    public static double getTime() {
+        return _instance.dt * _instance.clock;
+    }
+
+    public static double getDt() {
+        return _instance.dt;
+    }
+
+    public static void setDt(double dt) {
+        _instance.dt = dt;
+    }
+    
+    public static void step() {
+        _instance.clock++;
+    }
+}

diff -N ClockDriver.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ClockDriver.java	29 Aug 2011 23:03:20 -0000	1.1
@@ -0,0 +1,24 @@

+/*
+ * To change this template, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package org.lcsim.hps.util;
+
+import org.lcsim.event.EventHeader;
+import org.lcsim.util.Driver;
+
+/**
+ * Driver to run the clock in ClockSingleton. Run this driver last.
+ * 
+ * @author Sho Uemura <[log in to unmask]>
+ * @version $Id: ClockDriver.java,v 1.1 2011/08/29 23:03:20 meeg Exp $
+ */
+public class ClockDriver extends Driver {
+    public void setDt(double dt) {
+        ClockSingleton.setDt(dt);
+    }
+
+    public void process(EventHeader event) {
+        ClockSingleton.step();
+    }
+}