Hi reyalp,
Have a look at this one (attached). I changed it to iso20 to iso200
...... john
From the sv column, this only ran from 20 to 78. As expected, there's no meaningful change in the exposure, meter bounces around between 132 and 133. Generally CHDK ISO overrides are not effective much below the stock minimum ISO.
If you run it again, I suggest setting "ISO set mode" to "CHDK" rather than script. "Script" was a test case for weird issues on certain camera.