diff --git a/app/src/main/java/com/philliphsu/clock2/DaysOfWeek.java b/app/src/main/java/com/philliphsu/clock2/DaysOfWeek.java
index fa179d9..38d7bd4 100644
--- a/app/src/main/java/com/philliphsu/clock2/DaysOfWeek.java
+++ b/app/src/main/java/com/philliphsu/clock2/DaysOfWeek.java
@@ -3,6 +3,7 @@ package com.philliphsu.clock2;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
+import android.support.annotation.VisibleForTesting;
 import android.util.Log;
 
 import java.util.Arrays;
@@ -57,11 +58,21 @@ public class DaysOfWeek {
         return sAppContext.getString(LABELS_RES[weekDay]);
     }
 
-    /** @return the week day whose order is specified by {@code ordinalDay} */
-    public int weekDay(int ordinalDay) {
-        if (ordinalDay < 0 || ordinalDay > 6)
+    /** @return the week day at {@code position} within the user-defined week */
+    public int weekDay(int position) {
+        if (position < 0 || position > 6)
             throw new ArrayIndexOutOfBoundsException("Ordinal day out of range");
-        return DAYS[ordinalDay];
+        return DAYS[position];
+    }
+
+    /** @return the position of the {@code weekDay} within the user-defined week */
+    public int positionOf(int weekDay) {
+        if (weekDay < SUNDAY || weekDay > SATURDAY)
+            throw new ArrayIndexOutOfBoundsException("Week day ("+weekDay+") out of range");
+        for (int i = 0; i < DAYS.length; i++)
+            if (DAYS[i] == weekDay)
+                return i;
+        return -1;
     }
 
     @Override
@@ -71,7 +82,8 @@ public class DaysOfWeek {
                 + "}";
     }
 
-    private DaysOfWeek(int firstDayOfWeek) {
+    @VisibleForTesting
+    DaysOfWeek(int firstDayOfWeek) {
         if (firstDayOfWeek != SATURDAY && firstDayOfWeek != SUNDAY && firstDayOfWeek != MONDAY)
             throw new IllegalArgumentException("Invalid first day of week: " + firstDayOfWeek);
         DAYS[0] = firstDayOfWeek;
diff --git a/app/src/test/java/com/philliphsu/clock2/DaysOfWeekTest.java b/app/src/test/java/com/philliphsu/clock2/DaysOfWeekTest.java
new file mode 100644
index 0000000..96cd306
--- /dev/null
+++ b/app/src/test/java/com/philliphsu/clock2/DaysOfWeekTest.java
@@ -0,0 +1,74 @@
+package com.philliphsu.clock2;
+
+import org.junit.Test;
+
+import static com.philliphsu.clock2.DaysOfWeek.*;
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Created by Phillip Hsu on 6/1/2016.
+ */
+public class DaysOfWeekTest {
+
+    @Test
+    public void testSundayAsFirstDayOfWeek() {
+        DaysOfWeek days = new DaysOfWeek(SUNDAY);
+        assertEquals(days.weekDay(0), SUNDAY);
+        assertEquals(days.weekDay(1), MONDAY);
+        assertEquals(days.weekDay(2), TUESDAY);
+        assertEquals(days.weekDay(3), WEDNESDAY);
+        assertEquals(days.weekDay(4), THURSDAY);
+        assertEquals(days.weekDay(5), FRIDAY);
+        assertEquals(days.weekDay(6), SATURDAY);
+
+        assertEquals(days.positionOf(SUNDAY), 0);
+        assertEquals(days.positionOf(MONDAY), 1);
+        assertEquals(days.positionOf(TUESDAY), 2);
+        assertEquals(days.positionOf(WEDNESDAY), 3);
+        assertEquals(days.positionOf(THURSDAY), 4);
+        assertEquals(days.positionOf(FRIDAY), 5);
+        assertEquals(days.positionOf(SATURDAY), 6);
+    }
+
+    @Test
+    public void testSaturdayAsFirstDayOfWeek() {
+        DaysOfWeek days = new DaysOfWeek(SATURDAY);
+        assertEquals(days.weekDay(0), SATURDAY);
+        assertEquals(days.weekDay(1), SUNDAY);
+        assertEquals(days.weekDay(2), MONDAY);
+        assertEquals(days.weekDay(3), TUESDAY);
+        assertEquals(days.weekDay(4), WEDNESDAY);
+        assertEquals(days.weekDay(5), THURSDAY);
+        assertEquals(days.weekDay(6), FRIDAY);
+
+        assertEquals(days.positionOf(SUNDAY), 1);
+        assertEquals(days.positionOf(MONDAY), 2);
+        assertEquals(days.positionOf(TUESDAY), 3);
+        assertEquals(days.positionOf(WEDNESDAY), 4);
+        assertEquals(days.positionOf(THURSDAY), 5);
+        assertEquals(days.positionOf(FRIDAY), 6);
+        assertEquals(days.positionOf(SATURDAY), 0);
+    }
+
+    @Test
+    public void testMondayAsFirstDayOfWeek() {
+        DaysOfWeek days = new DaysOfWeek(MONDAY);
+        assertEquals(days.weekDay(0), MONDAY);
+        assertEquals(days.weekDay(1), TUESDAY);
+        assertEquals(days.weekDay(2), WEDNESDAY);
+        assertEquals(days.weekDay(3), THURSDAY);
+        assertEquals(days.weekDay(4), FRIDAY);
+        assertEquals(days.weekDay(5), SATURDAY);
+        assertEquals(days.weekDay(6), SUNDAY);
+
+        assertEquals(days.positionOf(SUNDAY), 6);
+        assertEquals(days.positionOf(MONDAY), 0);
+        assertEquals(days.positionOf(TUESDAY), 1);
+        assertEquals(days.positionOf(WEDNESDAY), 2);
+        assertEquals(days.positionOf(THURSDAY), 3);
+        assertEquals(days.positionOf(FRIDAY), 4);
+        assertEquals(days.positionOf(SATURDAY), 5);
+
+        System.out.println(days.toString());
+    }
+}