@epierre Now I see your point of view and of course it is better way to reduce the error.
in the other hand, I found the datasheet in chinese an then a friend translate it.
the meaning of the name of gases is for 3/4 (Alcohol), 1/4 (Tolueno) or +- (acetona)
Thank you so much.
@epierre
Hi, May be I do not explain my point correctly (or maybe I misundertood ), let me try again.
We adopt a code, which is the next. The blue lines are the points (for each gas we need two points) that we need.
https://docs.google.com/document/d/1CevnhBLL9uoyZ31kkrMn-SXeOF_4e9YFGmchj46pGPY/edit?usp=sharing
Specifically we read from the datasheet the pairs of points for CO
point1 (lg200 , lg1.3)
Point2 (lg10, lg2.9)
then, we construct the data format:{ x, y, slope};
COCurve[3] = {1.0,0.462,-0.268};
We are wondering about the pair of points for the others gases or the { x, y, slope} data for them, could you share them?.
and the other hand, the name of gases with 3/4 or 1/4 or +- appears as well in your datasheet (figure 3)... do you know why?
thank you so much
@epierre Hi...it is ameasing your work 
I am wondering about Mq-135. We have troubles with reading differents gases.
From the datasheet we read the slopes
Gas X" X0" "Rs/R0 "Rs/R0 pendiente (log y- log y0)/(log x-log x0)"
Air 200 10 3.6 3.6 0.00000
co 200 10 1.3 2.9 -0.26783
nh4 200 10 0.79 2.7 -0.41024
c02 200 10 0.8 2.4 -0.36673
3/4/ 200 10 0.72 1.9 -0.32391
1/4/ 200 10 0.64 1.5 -0.28432
+- 200 10 0.59 1.4 -0.28845
the data are in the next worksheet https://docs.google.com/spreadsheets/d/18Z6XyxwXVsWdMIk9vbUuCucaLJDdmR0QUFSTYG79ftw/edit?usp=sharing
¿may you share with us your code for this sensor in order to see your slopes and Rs/R0 values ?
¿do you know the meaning of the name of gases with 3/4 or 1/4 or +-
thank you in advance
@epierre Hi...it is ameasing your work!!
I am wondering about Mq-135. We have troubles with reading differents gases.
From the datasheet we read the slopes
Gas X" X0" "Rs/R0 "Rs/R0 pendiente (log y- log y0)/(log x-log x0)"
Air 200 10 3.6 3.6 0.00000
co 200 10 1.3 2.9 -0.26783
nh4 200 10 0.79 2.7 -0.41024
c02 200 10 0.8 2.4 -0.36673
3/4/ 200 10 0.72 1.9 -0.32391
1/4/ 200 10 0.64 1.5 -0.28432
+- 200 10 0.59 1.4 -0.28845
these data are in the next worksheet https://docs.google.com/spreadsheets/d/18Z6XyxwXVsWdMIk9vbUuCucaLJDdmR0QUFSTYG79ftw/edit?usp=sharing
¿may you share with us your code for this sensor in order to see your slopes and Rs/R0 values taken from the curve?
¿do you know the meaning of the name go gases with 3/4 or 1/4 or +- ?
thank you in advance