diff --git a/README.md b/README.md
index 95b08cf..41211f2 100644
--- a/README.md
+++ b/README.md
@@ -81,7 +81,7 @@ int sensorMovingAvg = mySensor.getAvg();
 
 ### getAvg(int nPoints)
 ##### Description
-Like `getAvg()` except only uses the most recent `nPoints` data points to calculate the average. This allows calculation of shorter term and longer term averages. If `nPoints` is less than one, or larger than the number of points given in the constructor, then the overall average is returned, i.e. the same value as `getAvg()` would return.
+Like `getAvg()` except only uses the most recent `nPoints` data points to calculate the average. This allows calculation of shorter term and longer term averages. If `nPoints` is less than one, or larger than the number of points given in the constructor, or larger than the number of data points so far accumulated, then zero is returned.
 ##### Syntax
 `getAvg(nPoints);`
 ##### Parameters
diff --git a/examples/Subset/Subset.ino b/examples/Subset/Subset.ino
index 532c92f..b65db86 100644
--- a/examples/Subset/Subset.ino
+++ b/examples/Subset/Subset.ino
@@ -3,40 +3,62 @@
 // Copyright (C) 2020 by Jack Christensen and licensed under
 // GNU GPL v3.0, https://www.gnu.org/licenses/gpl.html
 //
-// Example sketch to demonstrate calculating shorter term averages
+// Example sketch to test/demonstrate calculating shorter term averages
 // from a subset of the data, using just the most recent data points.
 
-#include <movingAvg.h>          // https://github.com/JChristensen/movingAvg
+#include <movingAvg.h>      // https://github.com/JChristensen/movingAvg
+#include <Streaming.h>      // https://github.com/janelia-arduino/Streaming
 
-constexpr int arraySize {30};
+constexpr int arraySize{30};
 movingAvg foo(arraySize);
 
 void setup()
 {
     Serial.begin(115200);
+    Serial << F( "\n" __FILE__ "\nCompiled " __DATE__ " " __TIME__ "\n\n" );
     foo.begin();
 
-    // generate some sample data
-    for (int i=1; i<=arraySize; ++i) {
+    // generate sample data, more points than interval size
+    for (int i=1; i<=42; ++i) {
         foo.reading(i);
     }
 
-    Serial.print("Average overall: ");
-    Serial.println(foo.getAvg());
-    Serial.print("Average last 10: ");
-    Serial.println(foo.getAvg(10));
-    Serial.print("Average last 3:  ");
-    Serial.println(foo.getAvg(3));
-    Serial.print("Average last 2:  ");
-    Serial.println(foo.getAvg(2));
-    Serial.print("Average last 1:  ");
-    Serial.println(foo.getAvg(1));
-    Serial.print("Average last 0:  ");
-    Serial.println(foo.getAvg(0));
-    Serial.print("Average last 30: ");
-    Serial.println(foo.getAvg(30));
-    Serial.print("Average last 31: ");
-    Serial.println(foo.getAvg(31));
+    avgTest("Average overall", foo.getAvg(),   28);
+    avgTest("Average last 10", foo.getAvg(10), 38);
+    avgTest("Average last 3 ", foo.getAvg(3),  41);
+    avgTest("Average last 2 ", foo.getAvg(2),  42);
+    avgTest("Average last 1 ", foo.getAvg(1),  42);
+    avgTest("Average last 0 ", foo.getAvg(0),   0);
+    avgTest("Average last 30", foo.getAvg(30), 28);
+    avgTest("Average last 31", foo.getAvg(31),  0);
+
+    Serial << endl;
+    foo.reset();
+    // generate sample data, fewer points than interval size
+    for (int i=1; i<=17; ++i) {
+        foo.reading(i);
+    }
+    avgTest("Average overall", foo.getAvg(),    9);
+    avgTest("Average last 10", foo.getAvg(10), 13);
+    avgTest("Average last 3 ", foo.getAvg(3),  16);
+    avgTest("Average last 2 ", foo.getAvg(2),  17);
+    avgTest("Average last 1 ", foo.getAvg(1),  17);
+    avgTest("Average last 0 ", foo.getAvg(0),   0);
+    avgTest("Average last 30", foo.getAvg(30),  0);
+    avgTest("Average last 31", foo.getAvg(31),  0);
+    avgTest("Average last 17", foo.getAvg(17),  9);
+}
+
+// function to compare the average returned by the library to the known correct value
+void avgTest(const char* msg, int val, int correctVal)
+{
+    Serial << msg << ": " << val << " ... ";
+    if (val == correctVal) {
+        Serial << "OK\n";
+    }
+    else {
+        Serial << "ERROR, expected " << correctVal << endl;
+    }
 }
 
 void loop() {}
diff --git a/library.properties b/library.properties
index eb4c02f..230891e 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=movingAvg
-version=2.3.0
+version=2.3.1
 author=Jack Christensen <jack.christensen@outlook.com>
 maintainer=Jack Christensen <jack.christensen@outlook.com>
 sentence=A simple Arduino library for calculating moving averages.
diff --git a/src/movingAvg.cpp b/src/movingAvg.cpp
index c11808b..b9a46ab 100644
--- a/src/movingAvg.cpp
+++ b/src/movingAvg.cpp
@@ -36,15 +36,22 @@ int movingAvg::getAvg()
 }
 
 // return the average for a subset of the data, the most recent nPoints readings.
-// for invalid values of nPoints, just return the overall average.
+// for invalid values of nPoints, return zero.
 int movingAvg::getAvg(int nPoints)
 {
-    if (nPoints < 1 || nPoints > m_interval - 1) {
-        return (m_sum + m_nbrReadings / 2) / m_nbrReadings;
+    if (nPoints < 1 || nPoints > m_interval || nPoints > m_nbrReadings) {
+        return 0;
     }
     else {
-        long sum {0};
-        for (int i=m_nbrReadings-1; i>=m_nbrReadings-nPoints; --i) {
+        long sum{0};
+        int i = m_next;
+        for (int n=0; n<nPoints; ++n) {
+            if (i == 0) {
+                i = m_interval - 1;
+            }
+            else {
+                --i;
+            }
             sum += m_readings[i];
         }
         return (sum + nPoints / 2) / nPoints;
diff --git a/src/movingAvg.h b/src/movingAvg.h
index 580db4d..dadd2c3 100644
--- a/src/movingAvg.h
+++ b/src/movingAvg.h
@@ -10,7 +10,7 @@ class movingAvg
 {
     public:
         movingAvg(int interval)
-            : m_interval(interval), m_nbrReadings(0), m_sum(0), m_next(0) {}
+            : m_interval{interval}, m_nbrReadings{0}, m_sum{0}, m_next{0} {}
         void begin();
         int reading(int newReading);
         int getAvg();