README.md in standard_deviation-0.0.1 vs README.md in standard_deviation-1.0.0

@@ -16,28 +16,39 @@
 
     $ gem install standard_deviation
 
 ## Usage
 
-Just call `standard_deviation` or `stdev` on a array with numbers.
+Just call `standard_deviation` or `stdev` on an array with numbers:
 
 ``` ruby
 [1, 2, 3, 4, 5].stdev => 1.5811388300841898
 
 [521.0, BigDecimal("1234.45"), 1_120].standard_deviation => 383.168958598336
 ```
+For population standard deviation, call `stdevp`:
 
+``` ruby
+[1, 2, 3, 4, 5].stdevp => 1.4142135623730951
+```
+
+Also, the API exposes the `sample_variance` and `population_variance` calculations:
+``` ruby
+[1, 2, 3, 4, 5].sample_variance => 2.5
+[1, 2, 3, 4, 5].population_variance => 2.0
+```
+
 ## Benchmarks
 
 ``` ruby
 # Basic ruby implementation
 class Array
   def stdev_ruby
     total = inject :+
     mean  = total.to_f / size
-    variance = inject(0) { |variance, value| variance + (value - mean) ** 2 }
+    variance = inject(0) { |variance, value| variance + (value - mean) ** 2 } / (size - 1)
 
-    Math.sqrt(variance / (size - 1))
+    Math.sqrt(variance)
   end
 end
 
 # Running on a 2.4 GHz MacBook Pro
 n = 10000