Krodal:
This gives basic information : Arduino Playground - HomePageWhat you want is not possible.
The resistor is the only way to adjust the sensor output.You could use the resistor as "Adjust".
And you could use software for "Sensitivity", using the map() function : map() - Arduino ReferenceIf the bar on the LCD is the only output, it is very rough. The analogue value could easily be mapped for the LCD bar with the map() function.
Thanks for the replies, so far the sensor circuit wise is the same as the light sensor in the tutorials (or the MQ playground) and I have a speaker tracking the level. I'm trying to achieve a sensor that is functionally like a metal detector rather than a smoke alarm, but looks for a gas not metal.
The idea is to sweep for a leak on an ultra sensitive setting to find the general area, then drop the sensitivity down to pin point an accurate point as the source of the leak. However if the incoming value is de-sensitised the result on the bar graph will just drop too and that's kind of a 'catch 22' problem! 