hello!
i want to get a toluene PPM by using MQ138 sensor.
there are some sources on internet so i have used that.
but the output is not correct( i have another thing to get a toluene gas the name is YesAir device)
so i want to check that source codes are correct.
is there another guys have used MQ138 sensor?
i used this sources
https://gist.github.com/esmarr58/2e9335bfc64077407ed2286408982f61
i knew this site from this source. but i do not know how to get the curve and can not sure the initialized value. and some codes was not working such as

return  (long)((long)(1024*1000*(long)rl_value)/raw_adc-(long)rl_value);

https://gist.github.com/esmarr58/2e9335bfc64077407ed2286408982f61
i used this source. sure i changed curve to [1.7, -0.57, -0.5] and RL value to 4.7(from datasheet)
now i can get a PPM value but the values are 0.00006, 0.00008.....
MQ138 datasheet

i know this sensor's range is 5~500 PPM. so i want to check the code. that codes are correct?
and if that wrong, where should i get a correct source code..?
waiting anything.
regard.