diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6357aeb..0181ec3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.4.7] - 2024-08-12
+- Fix #33, add **float getCoefficientOfVariation()**
+- update readme.md
+- update keywords.txt
+
 ## [0.4.6] - 2024-06-15
 - Fix #30, add **float getSum()** (thanks to heidnerd)
 - Fix #31, add **float getStandardDeviationLast(uint16_t count)** (thanks to alvaro-oliver)
diff --git a/README.md b/README.md
index e7bbfc2..ff06d81 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ update the internal **\_sum**.
 - https://github.com/RobTillaart/RunningMedian
 - https://github.com/RobTillaart/statHelpers - combinations & permutations
 - https://github.com/RobTillaart/Statistic
+- https://github.com/RobTillaart/Student
 
 
 ## Interface
@@ -83,8 +84,14 @@ Updates the variables used by **getFastAverage()** to improve its accuracy again
 - **float getStandardDeviation()** returns the standard deviation of the current content. 
 Needs more than one element to be calculable.
 - **float getStandardError()** returns the standard error of the current content.
-- **float getMin()** returns minimum since last clear, does not need to be in the buffer any more.
-- **float getMax()** returns maximum since last clear, does not need to be in the buffer any more.
+- **float getCoefficientOfVariation()** returns coefficient of variation.
+This is defined as standardDeviation / Average. 
+It indicates if the distribution is relative small ( < 1) or relative wide ( > 1).
+Note it has no meaning when the average is zero (or close to zero).
+- **float getMin()** returns minimum since last call to clear(). 
+The returned value does not need to be in the buffer any more.
+- **float getMax()** returns maximum since last call to clear(). 
+The returned value does not need to be in the buffer any more.
 - **float getMinInBuffer()** returns minimum in the internal buffer.
 - **float getMaxInBuffer()** returns maximum in the internal buffer.
 - **float getSum()** returns sum of values in the internal buffer.
@@ -94,7 +101,7 @@ Needs more than one element to be calculable.
 
 - **bool bufferIsFull()** returns true if buffer is full.
 - **float getElement(uint16_t index)** get element directly from internal buffer at index. (debug)
-- **uint16_t getSize()** returns the size of the internal array.
+- **uint16_t getSize()** returns the size of the internal array as set in constructor.
 - **uint16_t getCount()** returns the number of slots used of the internal array.
 
 
@@ -114,6 +121,7 @@ Returns NAN if there are no elements and it will reduce count if there are less
 count elements in the buffer.
 
 - **float getAverageLast(uint16_t count)** get the average of the last count elements.
+- **float getStandardDeviationLast(uint16_t count)** get the stddev of the last count elements.
 - **float getMinInBufferLast(uint16_t count)** get the minimum of the last count elements.
 - **float getMaxInBufferLast(uint16_t count)** get the maximum of the last count elements.
 
@@ -174,22 +182,14 @@ See examples
 #### Should
 
 - check for optimizations.
-  - divide by count happens often
-  - fillValue can be optimized (See #13)
-- ```temp = sqrt(temp/(_count - 1));```  is this correct STDDEV?
-  - divide by count or count - 1?  
-  - https://www.zaner.com/3.0/education/technicalstudies/MSD.asp
-  
+  - divide by count (-1) happens often.
+  - fillValue can be optimized (See #13).
+
 #### Could
 
 - create a double based derived class? 
   - Template class?
 - add error handling (important?).
-- investigate **modus()** most frequently occurring value.
-  - difficult with floats ?
-  - what to do when on two or more values are on par? (no modus?)
-- **int getUniqueValuesInBuffer()** O(n^2)
-
 
 #### Wont
 
@@ -198,6 +198,10 @@ See examples
 - clear(bool zero = true) to suppress setting all to 0. ?
   - makes **addValue()** slightly more complex
   - could introduce conflicts due to randomness data?
+- investigate **modus()** most frequently occurring value.
+  - difficult with floats ?
+  - what to do when on two or more values are on par? (no modus?)
+- **int getUniqueValuesInBuffer()** O(n^2).
 
 
 ## Support
diff --git a/RunningAverage.cpp b/RunningAverage.cpp
index 795dcb4..92afbc7 100644
--- a/RunningAverage.cpp
+++ b/RunningAverage.cpp
@@ -1,7 +1,7 @@
 //
 //    FILE: RunningAverage.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.4.6
+// VERSION: 0.4.7
 //    DATE: 2011-01-30
 // PURPOSE: Arduino library to calculate the running average by means of a circular buffer
 //     URL: https://github.com/RobTillaart/RunningAverage
@@ -140,7 +140,7 @@ float RunningAverage::getMaxInBuffer() const
 
 
 //  returns the value of an element if exist, NAN otherwise
-float RunningAverage::getElement(uint16_t index) const
+float RunningAverage::getElement(const uint16_t index) const
 {
   if ((_count == 0) || (_array == NULL))
   {
@@ -166,7 +166,9 @@ float RunningAverage::getStandardDeviation() const
   {
     temp += pow((_array[i] - average), 2);
   }
-  //  TODO: when to divide by count || count-1?
+  //  when to divide by count || count-1?
+  //  - divide by count: whole set
+  //  - divide by count - 1: sample of larger set (which run avg is)
   temp = sqrt(temp/(_count - 1));
   return temp;
   //  see issue #13
@@ -191,6 +193,19 @@ float RunningAverage::getStandardError() const
 }
 
 
+//  Return coefficient of variation.
+//  If buffer is empty or has only one element or zero average, return NAN.
+float RunningAverage::getCoefficientOfVariation() const
+{
+  float temp = getStandardDeviation();
+  if (temp == NAN) return NAN;
+  if (_sum == 0) return NAN;
+
+  float cv = temp * _count / _sum;
+  return cv;
+}
+
+
 //  fill the average with the same value number times. (weight)
 //  This is maximized to size times.
 //  no need to fill the internal buffer over 100%
@@ -256,7 +271,7 @@ bool RunningAverage::setPartial(const uint16_t partial)
 }
 
 
-float RunningAverage::getAverageLast(uint16_t count)
+float RunningAverage::getAverageLast(const uint16_t count)
 {
   uint16_t cnt = count;
   if (cnt > _count) cnt = _count;
@@ -274,7 +289,7 @@ float RunningAverage::getAverageLast(uint16_t count)
 }
 
 
-float RunningAverage::getStandardDeviationLast(uint16_t count)
+float RunningAverage::getStandardDeviationLast(const uint16_t count)
 {
   uint16_t cnt = count;
   if (cnt > _count) cnt = _count;
@@ -296,7 +311,7 @@ float RunningAverage::getStandardDeviationLast(uint16_t count)
 }
 
 
-float RunningAverage::getMinInBufferLast(uint16_t count)
+float RunningAverage::getMinInBufferLast(const uint16_t count)
 {
   uint16_t cnt = count;
   if (cnt > _count) cnt = _count;
@@ -316,7 +331,7 @@ float RunningAverage::getMinInBufferLast(uint16_t count)
 }
 
 
-float RunningAverage::getMaxInBufferLast(uint16_t count)
+float RunningAverage::getMaxInBufferLast(const uint16_t count)
 {
   uint16_t cnt = count;
   if (cnt > _count) cnt = _count;
@@ -336,7 +351,7 @@ float RunningAverage::getMaxInBufferLast(uint16_t count)
 }
 
 
-float RunningAverage::getAverageSubset(uint16_t start, uint16_t count)
+float RunningAverage::getAverageSubset(const uint16_t start, const uint16_t count)
 {
   if ((_count == 0) || (_array == NULL))
   {
diff --git a/RunningAverage.h b/RunningAverage.h
index dd244ca..d9f11ff 100644
--- a/RunningAverage.h
+++ b/RunningAverage.h
@@ -2,7 +2,7 @@
 //
 //    FILE: RunningAverage.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.4.6
+// VERSION: 0.4.7
 //    DATE: 2011-01-30
 // PURPOSE: Arduino library to calculate the running average by means of a circular buffer
 //     URL: https://github.com/RobTillaart/RunningAverage
@@ -14,7 +14,7 @@
 #include "Arduino.h"
 
 
-#define RUNNINGAVERAGE_LIB_VERSION    (F("0.4.6"))
+#define RUNNINGAVERAGE_LIB_VERSION    (F("0.4.7"))
 
 
 class RunningAverage
@@ -36,6 +36,7 @@ class RunningAverage
   //  return statistical characteristics of the running average
   float    getStandardDeviation() const;
   float    getStandardError() const;
+  float    getCoefficientOfVariation() const;
 
   //  returns min/max added to the data-set since last clear
   float    getMin() const { return _min; };
@@ -49,7 +50,7 @@ class RunningAverage
   //  return true if buffer is full
   bool     bufferIsFull() const { return _count == _size; };
 
-  float    getElement(uint16_t index) const;
+  float    getElement(const uint16_t index) const;
 
   uint16_t getSize() const { return _size; }
   uint16_t getCount() const { return _count; }
@@ -61,13 +62,13 @@ class RunningAverage
 
 
   //  get some stats from the last count additions.
-  float    getAverageLast(uint16_t count);
-  float    getStandardDeviationLast(uint16_t count);
-  float    getMinInBufferLast(uint16_t count);
-  float    getMaxInBufferLast(uint16_t count);
+  float    getAverageLast(const uint16_t count);
+  float    getStandardDeviationLast(const uint16_t count);
+  float    getMinInBufferLast(const uint16_t count);
+  float    getMaxInBufferLast(const uint16_t count);
 
   //       Experimental 0.4.3
-  float    getAverageSubset(uint16_t start, uint16_t count);
+  float    getAverageSubset(const uint16_t start, const uint16_t count);
 
 
 protected:
diff --git a/examples/ra_getCoefficientOfVariation/ra_getCoefficientOfVariation.ino b/examples/ra_getCoefficientOfVariation/ra_getCoefficientOfVariation.ino
new file mode 100644
index 0000000..533079d
--- /dev/null
+++ b/examples/ra_getCoefficientOfVariation/ra_getCoefficientOfVariation.ino
@@ -0,0 +1,95 @@
+//
+//    FILE: ra_getCoefficientOfVariation.ino
+//  AUTHOR: Rob Tillaart
+// PURPOSE: show working of runningAverage
+//     URL: https://github.com/RobTillaart/RunningAverage
+
+
+#include "RunningAverage.h"
+
+
+RunningAverage myRA(10);
+int samples = 0;
+
+
+RunningAverage A(60);
+RunningAverage B(60);
+RunningAverage C(60);
+
+
+void setup(void)
+{
+  Serial.begin(115200);
+  Serial.println();
+  Serial.println(__FILE__);
+  Serial.print("RUNNINGAVERAGE_LIB_VERSION: ");
+  Serial.println(RUNNINGAVERAGE_LIB_VERSION);
+
+  myRA.clear();  //   explicitly start clean
+
+  for (int i = 0; i < 10; i++)
+  {
+    myRA.add(i * 0.01 + 1 );
+    Serial.print(myRA.getCount());
+    Serial.print("\t");
+    Serial.print(myRA.getAverage(), 3);
+    Serial.print("\t");
+    Serial.print(myRA.getStandardDeviation(), 3);
+    Serial.print("\t");
+    Serial.print(myRA.getStandardDeviation() / myRA.getAverage(), 3);
+    Serial.print("\t");
+    Serial.println(myRA.getCoefficientOfVariation(), 3);
+  }
+  Serial.println();
+
+
+  Serial.println();
+  Serial.println("Show effect of changing average and standard deviation.");
+  Serial.println("- A is reference");
+  Serial.println("- B has same stdev, distribution is 'smaller' (sharper)");
+  Serial.println("- C has same average, distribution is 'wider'");
+  Serial.println();
+
+  A.clear();
+  B.clear();
+  C.clear();
+
+  for (int i = 0; i <= 50; i++)
+  {
+    A.add((i - 25) * 1.0 + 100);  //  reference
+    B.add((i - 25) * 1.0 + 200);  //  change average
+    C.add((i - 25) * 3.0 + 100);  //  change stddev
+  }
+  Serial.println("\tA\tB\tC");
+  Serial.print("AVG\t");
+  Serial.print(A.getAverage(), 3);
+  Serial.print("\t");
+  Serial.print(B.getAverage(), 3);
+  Serial.print("\t");
+  Serial.println(C.getAverage(), 3);
+
+  Serial.print("STDEV\t");
+  Serial.print(A.getStandardDeviation(), 3);
+  Serial.print("\t");
+  Serial.print(B.getStandardDeviation(), 3);
+  Serial.print("\t");
+  Serial.println(C.getStandardDeviation(), 3);
+
+  Serial.print("COFVAR\t");
+  Serial.print(A.getCoefficientOfVariation(), 3);
+  Serial.print("\t");
+  Serial.print(B.getCoefficientOfVariation(), 3);
+  Serial.print("\t");
+  Serial.println(C.getCoefficientOfVariation(), 3);
+
+
+  delay(10000);
+}
+
+
+void loop(void)
+{
+}
+
+
+//  -- END OF FILE --
diff --git a/keywords.txt b/keywords.txt
index f15bef1..8d71be0 100644
--- a/keywords.txt
+++ b/keywords.txt
@@ -16,6 +16,7 @@ getAverage	KEYWORD2
 getFastAverage	KEYWORD2
 getStandardDeviation	KEYWORD2
 getStandardError	KEYWORD2
+getCoefficientOfVariation	KEYWORD2
 
 getMin	KEYWORD2
 getMax	KEYWORD2
@@ -23,7 +24,7 @@ getMinInBuffer	KEYWORD2
 getMaxInBuffer	KEYWORD2
 getSum	KEYWORD2
 
-bufferIsFull()	KEYWORD2
+bufferIsFull	KEYWORD2
 getElement	KEYWORD2
 getSize	KEYWORD2
 getCount	KEYWORD2
diff --git a/library.json b/library.json
index e01570e..2c03001 100644
--- a/library.json
+++ b/library.json
@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/RunningAverage.git"
   },
-  "version": "0.4.6",
+  "version": "0.4.7",
   "license": "MIT",
   "frameworks": "*",
   "platforms": "*",
diff --git a/library.properties b/library.properties
index 64fc2f9..6683ffa 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=RunningAverage
-version=0.4.6
+version=0.4.7
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=The library stores the last N individual values in a circular buffer to calculate the running average. 
diff --git a/performance.txt b/performance.txt
deleted file mode 100644
index c725453..0000000
--- a/performance.txt
+++ /dev/null
@@ -1,28 +0,0 @@
-
---------------------------------------
-
-Arduino UNO
-IDE 1.8.12
-
-Performance RunningAverage lib: 0.3.0
-
-	clear 		: 80
-	addValue 	: 24
-	fillValue 	: 1548
-	getValue 	: 4
-	getAverage 	: 512
-	getFastAverage 	: 36
-	getStandardDeviation 	: 1832
-	getStandardError 	: 1896
-	getMin 		: 4
-	getMax 		: 4
-	getMinInBuffer 	: 212
-	getMaxInBuffer 	: 204
-	bufferIsFull 	: 8
-	getElement 	: 4
-	getSize 	: 8
-	getCount 	: 8
-
-done...
-
---------------------------------------
\ No newline at end of file