Update README.md

README.md

@@ -4,13 +4,13 @@ Using the BME680 to measure temperature, pressure, humidity and air quality.
 
 The sensor is used to get so-called Gas Resistance and then an Air Quality Index (IAQ) is determined from a combination of the readings of humidity and gas content of the air.
 
-The index comprises up to 25% for the humidity contribution and 75% for the gas contribution.
+The index is comprised of contributions from humidity by up to 25% and gas concentrations by up to 75%.
 
-Very low or high humidity is considered to result in an uncomfortable environment, with 40% being optimal. Therefore the humidity contribution to the IAQ is derived from a value that is 0 when RH is 0 and rises to 25% at 40% RH, above 40% RH the value falls to 0 at 100% RH, so in summary the RH quality scores peaks at 40% RH and falls to 0 either side of that value, with the final value scaled between 0 and 25%.
+The affect of humidity on the index is determined bby 40% being considered an ideal level, with 0% or 100% being considered to create an uncomfortable environment. Therefore the humidity contribution to the IAQ is derived from a value that is 0 when RH is 0 rising to 25% when hunidity is optimal at 40%, then above that, value falls to 0 at 100% RH. In summary, the RH quality scores peaks at 40% RH and falls to 0 either side of that value, with the final value scaled between 0 and 25%.
 
-For Gas it has been assumed that normal breathable air with no pollutants (adverse gases) corresponds to the sensors highest output of 300,000 ohms. The sensor outputs a Gas resistance value ranging from a low of 50,000 to a high of 500,000 and beyond. A linear relationship is assumed and the output scaled accordingly between 0 and 75%.
+For Gas it has been assumed that normal breathable air with no pollutants (adverse gases) corresponds to the sensors highest output of 50,000 ohms or more. The sensor normally outputs a Gas resistance value ranging from a low of 50ohm to a high of 50,000ohm and beyond. A linear relationship is assumed and the output scaled accordingly between 0 and 75% for the range 50-50,000 ohms.
 
-The result of humidity and gas indexes is a qualitative and a so-called IAQ - Indoor Air Quality index value scaled from 0-100% (where 100% is good). This is then scaled to 0-500 where a 500 value is bad and descriptive values applied in stages from good to hazardous air quality.
+The result of humidity and gas indexes is a qualitative and a so-called IAQ - Indoor Air Quality index value, which is then scaled from 0-100% (where 100% is good). This is then scaled again from 0-500 where a 500 value is bad and descriptive values applied in stages from good to hazardous air quality.
 
 There is no definitive (ISO Standard) method for calculating an IAQ.