Can't get purple air II above 94%

Hi, I may be a bit late in replying. We have some generalized criteria for the R2 of the channel A and B scatter plot with linear regression. If an R2 >= 0.9; we’ve been considering that ‘good’; an R2<0.9 but >0.7 something to watch, and if prolonged R2<.7 likely need to clean and/ or replace. We typically do a channel A / B linear regression weekly.
Here is a another good resource page on the community forum: