diff --git a/docs/images/grovegas.jpeg b/docs/images/grovegas.jpeg
deleted file mode 100644
index fdc0f8bd..00000000
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diff --git a/docs/images/mq2-5.jpeg b/docs/images/mq2-5.jpeg
new file mode 100644
index 00000000..40d3b468
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diff --git a/docs/images/mq3-9.jpeg b/docs/images/mq3-9.jpeg
new file mode 100644
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diff --git a/docs/images/mq9.jpeg b/docs/images/mq9.jpeg
deleted file mode 100644
index e782a73e..00000000
Binary files a/docs/images/mq9.jpeg and /dev/null differ
diff --git a/src/gas/README.txt b/src/gas/README.txt
index fab9cf4a..4eeab52b 100644
--- a/src/gas/README.txt
+++ b/src/gas/README.txt
@@ -1,6 +1,6 @@
-Grove - Gas Sensor(MQ-2)：Combustible Gas Smoke [middle sensitivity]
-Grove - Gas Sensor(MQ-3)：Alcohol and Benzine [HIGH sensitivity] Long warmup
+Grove - Gas Sensor(MQ-2)：Combustible Gas Smoke [medium sensitivity]
+Grove - Gas Sensor(MQ-3)：Alcohol and Benzine [high sensitivity] Long warm-up
 Grove - Gas Sensor(MQ-5)：LPG, Natural Gas, Town Gas [high sensitivity]
 Grove - Gas Sensor(MQ-9)：LPG, CO, CH4 [low sensitivity]
 
-Note - Gas sensor need to be heated, first minute the data is incorrect.
+Note - Gas sensors need to be heated, first minute the data is incorrect.
diff --git a/src/gas/gas.cxx b/src/gas/gas.cxx
index 5ae91f1d..64415f1d 100644
--- a/src/gas/gas.cxx
+++ b/src/gas/gas.cxx
@@ -55,7 +55,7 @@ Gas::getSampledWindow (unsigned int freqMS, unsigned int numberOfSamples,
         return 0;
     }
 
-    // too much samples
+    // too many samples
     if (numberOfSamples > 0xFFFFFF) {
         return 0;
     }
diff --git a/src/gas/gas.h b/src/gas/gas.h
index 18ce111f..b32647c4 100644
--- a/src/gas/gas.h
+++ b/src/gas/gas.h
@@ -36,13 +36,17 @@ struct thresholdContext {
 namespace upm {
 
 /**
- * @brief gas sensor library
+ * @brief Gas Sensor Library
+ *
+ * Sensor Library for air quality and gas detecting sensors. Base class Gas provides buffered
+ * sampling, threshold checking, a basic printing function and a standard read function.
+ *
  * @defgroup gas libupm-gas
  */
 class Gas {
     public:
         /**
-         * Instanciates a Gas object
+         * Instantiates a Gas object
          *
          * @param gasPin pin where gas is connected
          */
@@ -57,9 +61,9 @@ class Gas {
          * Get samples from gas sensor according to provided window and
          * number of samples
          *
-         * @param freqMS time between each sample (in microseconds)
+         * @param freqMS time between each sample (in milliseconds)
          * @param numberOfSamples number of sample to sample for this window
-         * @param buffer bufer with sampled data
+         * @param buffer buffer with sampled data
          */
         virtual int getSampledWindow (unsigned int freqMS, unsigned int numberOfSamples, uint16_t * buffer);
 
@@ -70,12 +74,12 @@ class Gas {
          * @param ctx threshold context
          * @param threshold sample threshold
          * @param buffer buffer with samples
-         * @param len bufer len
+         * @param len buffer length
          */
         virtual int findThreshold (thresholdContext* ctx, unsigned int threshold, uint16_t * buffer, unsigned int len);
 
         /**
-         * Return avarage data for the sampled window
+         * Return average data for the sampled window
          *
          * @param ctx threshold context
          */
diff --git a/src/gas/mq2.h b/src/gas/mq2.h
index f1c1078e..b9619147 100644
--- a/src/gas/mq2.h
+++ b/src/gas/mq2.h
@@ -34,18 +34,18 @@ namespace upm {
      * The Grove - Gas Sensor (MQ2) module is useful for gas leakage detecting
      * (in home and industry). It can detect LPG, i-butane, methane, alcohol,
      * Hydrogen, smoke and other combustible gases. It's a medium sensitivity
-     * sensor with a detect concentration of 300-10000ppm.
+     * sensor with a detect concentration of 300-10000 ppm.
      *
      * @ingroup gas analog
      * @snippet mq2.cxx Interesting
-     * @image html grovegas.jpeg
+     * @image html mq2-5.jpeg
      */
     class MQ2 : public Gas {
         public:
             /**
              * MQ2 constructor
              *
-             * @param gasPin analog pin where sensor connected
+             * @param gasPin analog pin where sensor is connected
              */
             MQ2 (int gasPin);
 
diff --git a/src/gas/mq3.h b/src/gas/mq3.h
index 55f33546..49cefe05 100644
--- a/src/gas/mq3.h
+++ b/src/gas/mq3.h
@@ -33,19 +33,19 @@ namespace upm {
      *
      * The Grove MQ3 Gas Sensor module is useful for gas leakage detecting (in
      * home and industry). It can detect Alcohol Vapour and Benzine. It's
-     * highly sensitive but has a long warmup time of about 1minute. It's
-     * detect rate is of 0.04-4mg/L Alcohol.
+     * highly sensitive but has a long warm-up time of about 1 minute. It's
+     * detect rate is of 0.04-4 mg/L Alcohol.
      *
      * @ingroup gas analog
      * @snippet mq3.cxx Interesting
-     * @image html grovegas.jpeg
+     * @image html mq3-9.jpeg
      */
     class MQ3 : public Gas {
         public:
             /**
              * MQ3 constructor
              *
-             * @param gasPin analog pin where sensor connected
+             * @param gasPin analog pin where sensor is connected
              */
             MQ3 (int gasPin);
 
diff --git a/src/gas/mq5.h b/src/gas/mq5.h
index 2a517272..5adf7d0e 100644
--- a/src/gas/mq5.h
+++ b/src/gas/mq5.h
@@ -34,18 +34,18 @@ namespace upm {
      * The Grove - Gas Sensor (MQ5) module is useful for gas leakage detecting
      * (in home and industry). It can detect LPG, natural gas, town gas and so
      * on. It is highly sensitive and has a detection concentration of
-     * 300-10000ppm.
+     * 300-10000 ppm.
      *
      * @ingroup gas analog
      * @snippet mq5.cxx Interesting
-     * @image html grovegas.jpeg
+     * @image html mq2-5.jpeg
      */
     class MQ5 : public Gas {
         public:
             /**
              * MQ5 constructor
              *
-             * @param gasPin analog pin where sensor connected
+             * @param gasPin analog pin where sensor is connected
              */
             MQ5 (int gasPin);
 
diff --git a/src/gas/mq9.h b/src/gas/mq9.h
index e167fc1f..3e2145ab 100644
--- a/src/gas/mq9.h
+++ b/src/gas/mq9.h
@@ -33,18 +33,18 @@ namespace upm {
      *
      * The Grove MQ9 Gas Sensor module is useful for gas leakage detecting (in
      * home and industry). It can detect Carbon Monoxide, Coal Gas and
-     * Liquefied Gas. It's sensitivty is 10-1000ppmCO 100-10000PPm Gas.
+     * Liquefied Gas. It's sensitivity is 10-1000 ppm CO, 100-10000 ppm Gas.
      *
      * @ingroup gas analog
      * @snippet mq9.cxx Interesting
-     * @image html mq9.jpeg
+     * @image html mq3-9.jpeg
      */
     class MQ9 : public Gas {
         public:
             /**
              * Jhd1313m1 constructor
              *
-             * @param gasPin analog pin where sensor connected
+             * @param gasPin analog pin where sensor is connected
              */
             MQ9 (int gasPin);