How to decipher the gas_680/VOC data on PurpleAir Touch?

I’m looking at the “webpage” for my touch sensor, and I’m querying the JSON data and seeing this: gas_680 : 55.7

What exactly is gas_680? a TVOC (Total VOC) count? and what units is 55.7 in? :thinking:

That value is an Indoor Air Quality index value that is unitless, much like AQI generated from PM2.5 or ozone level. The level ranges from 0 to 500 in 50 point increments, with the highest level starting at 351. The breakdown is given in the datasheet on page 9. The components of the reference mixture are on the next page, but how those contribute to the index calculation is information proprietary to Bosch (gee, that sounds familiar!). Also note footnote 9 on page 9, which partly explains the rationale behind the index levels.