diff --git a/core/src/main/java/hudson/util/ClockDifference.java b/core/src/main/java/hudson/util/ClockDifference.java
new file mode 100644
index 0000000000000000000000000000000000000000..06e3e1fb13c0a67b063f6e4e2d34aac8b90a9fec
--- /dev/null
+++ b/core/src/main/java/hudson/util/ClockDifference.java
@@ -0,0 +1,53 @@
+package hudson.util;
+
+import hudson.Util;
+
+/**
+ * Represents a clock difference. Immutable.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public final class ClockDifference {
+    /**
+     * The difference in milliseconds.
+     *
+     * Positive value means the slave is behind the master,
+     * negative value means the slave is ahead of the master.
+     */
+    public final Long diff;
+
+    public ClockDifference(long value) {
+        this.diff = value;
+    }
+
+    /**
+     * Returns true if the difference is big enough to be considered dangerous.
+     */
+    public boolean isDangerous() {
+        return Math.abs(diff)>5000;
+    }
+
+    /**
+     * Gets the clock difference in HTML string.
+     */
+    public String toString() {
+        if(-1000<diff && diff <1000)
+            return "In sync";  // clock is in sync
+
+        long abs = Math.abs(diff);
+
+        String s = Util.getTimeSpanString(abs);
+        if(diff<0)
+            s += " ahead";
+        else
+            s += " behind";
+
+        return s;
+    }
+    
+    public String toHtml() {
+        String s = toString();
+        if(isDangerous())   s = "<span class=error>"+s+"</span>";
+        return s;
+    }
+}